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135 mhz quad if receiver data sheet ad6684 rev. 0 document feedback information furnished by analog devices is believed to be accurate and reliable. however, no responsibility is assumed by analog devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. specifications subject to change without notice. no license is granted by implication or otherwise under any patent or patent rights of analog devices. trademarks and registered trademarks are the property of their respective owners. o ne technology way, p.o. box 9106, norwood, ma 02062-9106, u.s.a. tel: 781.329.4700 ?2016 analog devices, inc. all rights reserved. technical support www.analog.com features jesd204b (subclass 1) coded serial digital outputs lane rates up to 15 gbps 1.68 w total power at 500 msps 420 mw per analog-to-digital converter (adc) channel sfdr = 82 dbfs at 305 mhz (1.8 v p-p input range) snr = 66.8 dbfs at 305 mhz (1.8 v p-p input range) noise density = ?151.5 dbfs/hz (1.8 v p-p input range) analog input buffer on-chip dithering to improve small signal linearity flexible differential input range 1.44 v p-p to 2.16 v p-p (1.80 v p-p nominal) 82 db channel isolation/crosstalk 0.975 v, 1.8 v, and 2.5 v dc supply operation noise shaping requantizer (nsr) option for main receiver variable dynamic range (vdr) option for digital predistortion (dpd) 4 integrated wideband digital downconverters (ddcs) 48-bit numerically controlled oscillator (nco), up to 4 cascaded half-band filters 1.4 ghz analog input full power bandwidth amplitude detect bits for efficient automatic gain control (agc) implementation differential clock input integer clock divide by 1, 2, 4, or 8 on-chip temperature diode flexible jesd204b lane configurations applications communications diversity multiband, multimode digital receivers 3g/4g, w-cdma, gsm, lte, lte-a hfc digital reverse path receivers digital predistortion observation paths general-purpose software radios functional block diagram clk+ clk? sdio sclk csb agnd ad6684 sysref clock generation 14 spi control 14 14 14 2 pdwn/stby jesd204b subclass 1 control fast detect vin+b vin?b 2 4 adc core buffer adc core signal monitor syncinbab vin+c vin?c fd_c fd_d serdoutcd0 serdoutcd1 serdoutab0 serdoutab1 vin+d vin?d signal processing tx outputs jesd204b high speed serializer syncinbcd avdd1 (0.975v) avdd2 (1.8v) drvdd1 (0.975v) dvdd (0.975v) avdd3 (2.5v) avdd1_sr (0.975v) spivdd (1.8v) drvdd2 (1.8v) digital downconverter (2) noise shaped requantizer (2) variable dynamic range (2) buffer 2 fast detect adc core buffer adc core signal monitor signal processing tx outputs jesd204b high speed serializer digital downconverter (2) noise shaped requantizer (2) variable dynamic range (2) buffer drgnd vin+a vin?a v cm_ab v cm_cd fd_a fd_b 8 signal monitor and fast detect 14994-001 figure 1.
ad6684 data sheet rev. 0 | page 2 of 107 table of contents features .............................................................................................. 1 ? applications ....................................................................................... 1 ? functional block diagram .............................................................. 1 ? revision history ............................................................................... 3 ? general description ......................................................................... 4 ? product highlights ........................................................................... 4 ? specifications ..................................................................................... 5 ? dc specifications ......................................................................... 5 ? ac specifications .......................................................................... 6 ? digital specifications ................................................................... 8 ? switching specifications .............................................................. 9 ? timing specifications .................................................................. 9 ? absolute maximum ratings .......................................................... 11 ? thermal characteristics ............................................................ 11 ? esd caution ................................................................................ 11 ? pin configuration and function descriptions ........................... 12 ? typical performance characteristics ........................................... 14 ? equivalent circuits ......................................................................... 21 ? theory of operation ...................................................................... 23 ? adc architecture ...................................................................... 23 ? analog input considerations .................................................... 23 ? voltage reference ....................................................................... 25 ? clock input considerations ...................................................... 26 ? temperature diode .................................................................... 27 ? adc overrange and fast detect .................................................. 28 ? adc overrange .......................................................................... 28 ? fast threshold detection (fd_a, fd_b, fd_c and fd_d) .... 28 ? signal monitor ................................................................................ 29 ? sport over jesd204b ............................................................. 29 ? digital downconverter (ddc) ..................................................... 32 ? ddc i/q input selection .......................................................... 32 ? ddc i/q output selection ....................................................... 32 ? ddc general description ........................................................ 32 ? frequency translation ................................................................... 38 ? general description ................................................................... 38 ? ddc nco + mixer loss and sfdr ........................................ 39 ? numerically controlled oscillator ........................................... 39 ? fir filters ........................................................................................ 41 ? general description ................................................................... 41 ? half-band filters ........................................................................ 42 ? ddc gain stage ......................................................................... 44 ? ddc complex to real conversion ......................................... 44 ? ddc example configurations ................................................. 45 ? noise shaping requantizer (nsr) ............................................... 49 ? decimating half-band filter .................................................... 49 ? nsr overview ............................................................................ 50 ? variable dynamic range (vdr) .................................................. 51 ? vdr real mode .......................................................................... 52 ? vdr complex mode ................................................................. 52 ? digital outputs ............................................................................... 54 ? introduction to the jesd204b interface ................................. 54 ? jesd204b overview .................................................................. 54 ? functional overview ................................................................. 56 ? jesd204b link establishment ................................................. 56 ? physical layer (driver) outputs .............................................. 57 ? jesd204b tx converter mapping ........................................... 59 ? setting up the ad6684 digital interface ................................ 60 ? latency ............................................................................................. 64 ? end-to-end total latency ........................................................ 64 ? multichip synchronization ............................................................ 65 ? sysref setup/hold window monitor ................................. 67 ? test modes ....................................................................................... 69 ? adc test modes ........................................................................ 69 ? jesd204b block test modes .................................................... 70 ? serial port interface ........................................................................ 72 ? configuration using the spi ..................................................... 72 ? hardware interface ..................................................................... 72 ? spi accessible features .............................................................. 72 ? memory map .................................................................................. 73 ? reading the memory map register table ............................... 73 ? memory map .................................................................................. 74 ? memory map summary ............................................................ 74 ? memory map details ................................................................. 82 ? applications information ............................................................ 106 ? power supply recommendations ........................................... 106 ? exposed pad thermal heat slug recommendations .......... 106 ? avdd1_sr (pin 64) and agnd_sr (pin 63 and pin 67) . 106 ? outline dimensions ..................................................................... 107 ? ordering guide ........................................................................ 107 ?
data sheet ad6684 rev. 0 | page 3 of 107 revision history 10/2016revision 0: initial version
ad6684 data sheet rev. 0 | page 4 of 107 general description the ad6684 is a 135 mhz bandwidth, quad intermediate frequency (if) receiver. it consists of four 14-bit, 500 msps adcs and various digital processing blocks consisting of four wideband ddcs, an nsr, and vdr monitoring. the device has an on-chip buffer and a sample-and-hold circuit designed for low power, small size, and ease of use. this device is designed to support communications applications. the analog full power bandwidth of the device is 1.4 ghz. the quad adc cores feature a multistage, differential pipelined architecture with integrated output error correction logic. each adc features wide bandwidth inputs supporting a variety of user-selectable input ranges. an integrated voltage reference eases design considerations. the ad6684 is optimized for wide input bandwidth, excellent linearity, and low power in a small package. the analog inputs and clock signal input are differential. each pair of adc data outputs are internally connected to two ddcs through a crossbar mux. each ddc consists of up to five cascaded signal processing stages: a 48-bit frequency translator, nco, and up to four half-band decimation filters. each adc output is connected internally to an nsr block. the integrated nsr circuitry allows improved snr performance in a smaller frequency band within the nyquist bandwidth. the device supports two different output modes selectable via the serial port interface (spi). with the nsr feature enabled, the outputs of the adcs are processed such that the ad6684 supports enhanced snr performance within a limited portion of the nyquist bandwidth while maintaining a 9-bit output resolution. each adc output is also connected internally to a vdr block. this optional mode allows full dynamic range for defined input signals. inputs that are within a defined mask (based on dpd applications) are passed unaltered. inputs that violate this defined mask result in the reduction of the output resolution. with vdr, the dynamic range of the observation receiver is determined by a defined input frequency mask. for signals falling within the mask, the outputs are presented at the maximum resolution allowed. for signals exceeding defined power levels within this frequency mask, the output resolution is truncated. this mask is based on dpd applications and supports tunable real if sampling, and zero if or complex if receive architectures. operation of the ad6684 in the ddc, nsr, and vdr modes is selectable via spi-programmable profiles (the default mode is nsr at startup). in addition to the ddc blocks, the ad6684 has several functions that simplify the agc function in the communications receiver. the programmable threshold detector allows monitoring of the incoming signal power using the fast detect output bits of the adc. if the input signal level exceeds the programmable threshold, the fast detect indicator goes high. because this threshold indicator has low latency, the user can quickly turn down the system gain to avoid an overrange condition at the adc input. users can configure each pair of if receiver outputs onto either one or two lanes of subclass 1 jesd204b-based high speed serialized outputs, depending on the decimation ratio and the acceptable lane rate of the receiving logic device. multiple device synchronization is supported through the sysref, syncinbab, and syncinbcd input pins. the ad6684 has flexible power-down options that allow significant power savings when desired. all of these features can be programmed using the 1.8 v capable, 3-wire spi. the ad6684 is available in a pb-free, 72-lead lfcsp and is specified over the ?40c to +105c junction temperature range. this product may be protected by one or more u.s. or international patents product highlights 1. low power consumption per channel. 2. jesd204b lane rate support up to 15 gbps. 3. wide full power bandwidth supports if sampling of signals up to 1.4 ghz. 4. buffered inputs ease filter design and implementation. 5. four integrated wideband decimation filters and nco blocks supporting multiband receivers. 6. programmable fast overrange detection. 7. on-chip temperature diode for system thermal management.
data sheet ad6684 rev. 0 | page 5 of 107 specifications dc specifications avdd1 = 0.975 v, avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, drvdd2 = 1.8 v, spivdd = 1.8 v, specified maximum sampling rate, clock divider = 4, 1.8 v p-p full-scale differential input, 0.5 v internal ref erence, a in = ?1.0 dbfs, default spi settings, unless otherwise noted. minimum and maximum specifications are guaranteed for the full operati ng junction temperature (t j ) range of ?40c to +105c. typical specifications represent performance at t j = 50c (t a = 25c). table 1. parameter min typ max unit resolution 14 bits accuracy no missing codes guaranteed offset error 0 % fsr offset matching 0 % fsr gain error ?5.0 +5.0 % fsr gain matching 1.0 % fsr differential nonlinearity (dnl) ?0.7 0.4 +0.7 lsb integral nonlinearity (inl) ?5.1 1.0 +5.1 lsb temperature drift offset error 8 ppm/ c gain error 214 ppm/ c internal voltage reference voltage 0.5 v input referred noise 2.6 lsb rms analog inputs differential input voltage range (programmable) 1.44 1.80 2.16 v p-p common-mode voltage (v cm ) 1.34 v differential input capacitance 1.75 pf differential input resistance 200 analog input full power bandwidth 1.4 ghz power supply 1 avdd1 0.95 0.975 1.00 v avdd1_sr 0.95 0.975 1.00 v avdd2 1.71 1.8 1.89 v avdd3 2.44 2.5 2.56 v dvdd 0.95 0.975 1.00 v drvdd1 0.95 0.975 1.00 v drvdd2 1.71 1.8 1.89 v spivdd 1.71 1.8 1.89 v i avdd1 319 482 ma i avdd1_sr 21 53 ma i avdd2 438 473 ma i avdd3 87 103 ma i dvdd 2 145 198 ma i drvdd1 162 207 ma i drvdd2 23 29 ma i spivdd 1 1.6 ma power consumption total power dissipation (including output drivers) 2 1.68 1.94 w power-down dissipation 325 mw standby 3 1.20 w 1 power is measured at nsr, 28% bandwidth, l, m, and f = 222. 2 default mode, no de cimation enabled. for each link, l = 2, m = 2, and f = 2. 3 standby mode is controlled by the spi.
ad6684 data sheet rev. 0 | page 6 of 107 ac specifications avdd1 = 0.975 v, avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, drvdd2 = 1.8 v, spivdd = 1.8 v, specified maximum sampling rate, clock divider = 4, 1.8 v p-p full-scale differential input, 0.5 v internal ref erence, a in = ?1.0 dbfs, default spi settings, vdr mode (input mask not triggered), unless otherwise noted. minimum and maximum specification s are guaranteed for the full operating junction temperature (t j ) range of ?40c to +105c. typical specifications represent performance at t j = 50c (t a = 25c). table 2. parameter 1 analog input full scale = 1.44 v p-p analog input full scale = 1.80 v p-p analog input full scale = 2.16 v p-p unit min typ max min typ max min typ max analog input full scale 1.44 1.80 2.16 v p-p noise density 2 ?149.7 ?151.5 ?153.0 dbfs/hz signal-to-noise ratio (snr) 3 vdr mode f in = 10 mhz 65.4 67.1 68.4 dbfs f in = 155 mhz 65.3 64.8 67.0 68.3 dbfs f in = 305 mhz 65.2 66.8 68.0 dbfs f in = 450 mhz 65.0 66.6 67.8 dbfs f in = 765 mhz 64.8 66.5 67.5 dbfs f in = 985 mhz 64.5 66.0 66.9 dbfs 21% bandwidth (bw) mode (>105 mhz at 500 msps) f in = 10 mhz 72.1 73.8 75.1 dbfs f in = 155 mhz 71.8 73.5 74.8 dbfs f in = 305 mhz 71.9 73.5 74.7 dbfs f in = 450 mhz 71.6 73.2 74.4 dbfs f in = 765 mhz 71.0 72.7 73.7 dbfs f in = 985 mhz 70.6 72.1 73.0 dbfs 28% bw mode (>135 mhz at 500 msps) f in = 10 mhz 69.6 71.3 72.6 dbfs f in = 155 mhz 69.1 70.8 72.1 dbfs f in = 305 mhz 69.1 70.7 71.9 dbfs f in = 450 mhz 69.4 71.0 72.2 dbfs f in = 765 mhz 68.5 70.2 71.2 dbfs f in = 985 mhz 68.5 70.0 70.9 dbfs signal-to-noise-and-distortion ratio (sinad) 3 f in = 10 mhz 65.3 67.0 68.2 dbfs f in = 155 mhz 65.2 64.5 66.8 67.9 dbfs f in = 305 mhz 65.1 66.6 67.6 dbfs f in = 450 mhz 65.0 66.4 67.3 dbfs f in = 765 mhz 64.7 66.1 66.9 dbfs f in = 985 mhz 64.2 65.5 66.2 dbfs effective number of bits (enob) 3 f in = 10 mhz 10.5 10.8 11.0 bits f in = 155 mhz 10.5 10.4 10.8 10.9 bits f in = 305 mhz 10.5 10.7 10.9 bits f in = 450 mhz 10.5 10.7 10.8 bits f in = 765 mhz 10.4 10.6 10.8 bits f in = 985 mhz 10.3 10.6 10.7 bits
data sheet ad6684 rev. 0 | page 7 of 107 parameter 1 analog input full scale = 1.44 v p-p analog input full scale = 1.80 v p-p analog input full scale = 2.16 v p-p unit min typ max min typ max min typ max spurious-free dynamic range (sfdr) 3 f in = 10 mhz 89 90 80 dbfs f in = 155 mhz 89 75 85 77 dbfs f in = 305 mhz 82 82 78 dbfs f in = 450 mhz 82 83 77 dbfs f in = 765 mhz 77 75 72 dbfs f in = 985 mhz 82 79 76 dbfs spurious-free dynamic range (sfdr) at ?3 dbfs 3 f in = 10 mhz 94 94 86 dbfs f in = 155 mhz 94 90 82 dbfs f in = 305 mhz 89 90 83 dbfs f in = 450 mhz 87 86 84 dbfs f in = 765 mhz 82 80 77 dbfs f in = 985 mhz 85 82 79 dbfs worst harmonic, second or third 3 f in = 10 mhz ?89 ?90 ?80 dbfs f in = 155 mhz ?89 ?85 ?75 ?77 dbfs f in = 305 mhz ?82 ?82 ?78 dbfs f in = 450 mhz ?82 ?83 ?77 dbfs f in = 765 mhz ?77 ?75 ?72 dbfs f in = 985 mhz ?82 ?79 ?76 dbfs worst harmonic, second or third at ?3 dbfs 3 f in = 10 mhz ?94 ?94 ?86 dbfs f in = 155 mhz ?94 ?90 ?82 dbfs f in = 305 mhz ?89 ?90 ?83 dbfs f in = 450 mhz ?87 ?86 ?84 dbfs f in = 765 mhz ?82 ?80 ?77 dbfs f in = 985 mhz ?85 ?82 ?79 dbfs worst other, excluding second or third harmonic 3 f in = 10 mhz ?96 ?98 ?99 dbfs f in = 155 mhz ?97 ?97 ?86 ?97 dbfs f in = 305 mhz ?97 ?98 ?97 dbfs f in = 450 mhz ?95 ?96 ?96 dbfs f in = 765 mhz ?92 ?91 ?88 dbfs f in = 985 mhz ?90 ?89 ?86 dbfs two tone intermodulation distortion (imd), ain1 and ain2 = ?7 dbfs f in1 = 154 mhz, f in2 = 157 mhz ?93 ?90 ?84 dbfs f in1 = 302 mhz, f in2 = 305 mhz ?90 ?90 ?84 dbfs crosstalk 4 82 82 82 db full power bandwidth 5 1.4 1.4 1.4 ghz 1 see the an-835 application note , understanding high speed adc testing and evaluation , for definitions and for details on how these tests were completed. 2 noise density is measured wi th no analog input signal. 3 see table 9 for recommended settings for fu ll-scale voltage and bu ffer current setting. 4 crosstalk is measured at 155 mhz with a ?1.0 dbfs analog in put on one channel and no in put on the adjacent channel. 5 measured with circuit shown in figure 58.
ad6684 data sheet rev. 0 | page 8 of 107 digital specifications avdd1 = 0.975 v, avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, drvdd2 = 1.8 v, spivdd = 1.8 v, specified maximum sampling rate, clock divider = 4, 1.8 v p-p full-scale differential input, 0.5 v internal ref erence, a in = ?1.0 dbfs, default spi settings, unless otherwise noted. minimum and maximum specifications are guaranteed for the full operati ng junction temperature (t j ) range of ?40c to +105c. typical specifications represent performance at t j = 50c (t a = 25c). table 3. parameter min typ max unit clock inputs (clk+, clk?) logic compliance lvds/lvpecl differential input voltage 400 800 1600 mv p-p input common-mode voltage 0.69 v input resistance (differential) 32 k input capacitance 0.9 pf sysref inputs (sysref+, sysref?) 1 logic compliance lvds/lvpecl differential input voltage 400 800 1800 mv p-p input common-mode voltage 0.6 0.69 2.2 v input resistance (differential) 18 22 k input capacitance (single-ended per pin) 0.7 pf logic inputs (pdwn/stby) logic compliance cmos logic 1 voltage 0.65 spivdd v logic 0 voltage 0 0.35 spivdd v input resistance 10 m logic inputs (sdio, sclk, csb) logic compliance cmos logic 1 voltage 0.65 spivdd v logic 0 voltage 0 0.35 spivdd v input resistance 56 k logic output (sdio) logic compliance cmos logic 1 voltage (i oh = 800 a) spivdd ? 0.45 v v logic 0 voltage (i ol = 50 a) 0 0.45 v syncin input (syncinb+ab, syncinb?ab, syncinb+cd, syncinb?cd) logic compliance lvds/lvpecl/cmos differential input voltage 400 800 1800 mv p-p input common-mode voltage 0.6 0.69 2.2 v input resistance (differential) 18 22 k input capacitance (single-ended per pin) 0.7 pf logic outputs (fd_a, fd_b) logic compliance cmos logic 1 voltage 0.8 spivdd v logic 0 voltage 0 0.5 v input resistance 56 k digital outputs (serdoutx, x = ab0, ab1, cd0, and cd1) logic compliance cml differential output voltage 455.8 mv p-p short-circuit current (i d short ) 15 ma differential termination impedance 100 1 dc-coupled input only.
data sheet ad6684 rev. 0 | page 9 of 107 switching specifications avdd1 = 0.975 v, avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, drvdd2 = 1.8 v, spivdd = 1.8 v, specified maximum sampling rate, clock divider = 4, 1.8 v p-p full-scale differential input, 0.5 v internal ref erence, a in = ?1.0 dbfs, default spi settings, unless otherwise noted. minimum and maximum specifications are guaranteed for the full operati ng junction temperature (t j ) range of ?40c to +105c. typical specifications represent performance at t j = 50c (t a = 25c). table 4. parameter min typ max unit clock clock rate at clk+/clk? pins 0.3 2.4 ghz maximum sample rate 1 500 msps minimum sample rate 2 240 msps clock pulse width high 125 ps clock pulse width low 125 ps output parameters unit interval (ui) 3 62.5 100 ps rise time (t r ) (20% to 80% into 100 load) 31.25 ps fall time (t f ) (20% to 80% into 100 load) 31.37 ps phase-locked loop (pll) lock time 5 ms data rate per channel (nrz) 4 1.5625 10 15 gbps latency 5 pipeline latency 54 sample clock cycles fast detect latency 30 sample clock cycles aperture aperture delay (t a ) 160 ps aperture uncertainty (jitter, t j ) 44 fs rms out-of-range recovery time 1 sample clock cycles 1 the maximum sample rate is the clock rate after the divider. 2 the minimum sample rate operates at 240 msps with l = 2 or l = 1. refer to spi regist er 0x011a to reduce the threshold of the clock detect circuit. 3 baud rate = 1/ui. a subset of this range can be supported. 4 default l = 2. this number can be changed ba sed on the sample rate and decimation ratio. 5 no ddcs used. l = 2, m = 2, f = 2 for each link. timing specifications table 5. parameter test conditions/comments min typ max unit clk+ to sysref+ timing requirements see figure 3 t su_sr device clock to sysref+ setup time ?44.8 ps t h_sr device clock to sysref+ hold time 64.4 ps spi timing requirements see figure 4 t ds setup time between the data and th e rising edge of sclk 4 ns t dh hold time between the data and the rising edge of sclk 2 ns t clk period of the sclk 40 ns t s setup time between csb and sclk 2 ns t h hold time between csb and sclk 2 ns t high minimum period that sclk must be in a logic high state 10 ns t low minimum period that sclk must be in a logic low state 10 ns t access maximum time delay between falling edge of sclk and output data valid for a read operation 6 10 ns t dis_sdio time required for the sdio pin to switch from an output to an input relative to the csb rising edge (not shown in figure 4) 10 ns
ad6684 data sheet rev. 0 | page 10 of 107 timing diagrams n ? 53 n ? 52 n ? 51 n ? 50 n ? 1 sample n n + 1 aperture delay n ? 54 clk+ clk? analog input signal 14994-002 figure 2. data output timing (nsr mode, 21%, l, m, f = 222) clk+ clk? sysref+ sysref? t su_sr t h_sr 14994-003 figure 3. sysref setup and hold timing don?t care don?t care don?t care don?t care sdio sclk t s t dh t clk t ds t access t h r/w a14a13a12a11a10a9a8a7 d7d6d3d2d1d0 t low t high csb 14994-004 figure 4. serial port interface timing diagram
data sheet ad6684 rev. 0 | page 11 of 107 absolute maximum ratings table 6. parameter rating electrical avdd1 to agnd 1.05 v avdd1_sr to agnd 1.05 v avdd2 to agnd 2.00 v avdd3 to agnd 2.70 v dvdd to dgnd 1.05 v drvdd1 to drgnd 1.05 v drvdd2 to drgnd 2.00 v spivdd to agnd 2.00 v vinx to agnd ?0.3 v to avdd3 + 0.3 v clk to agnd ?0.3 v to avdd1 + 0.3 v sclk, sdio, csb to dgnd ?0.3 v to spivdd + 0.3 v pdwn/stby to dgnd ?0.3 v to spivdd + 0.3 v sysref to agnd_sr 0 v to 2.5 v syncinab/syncincd to drgnd 0 v to 2.5 v environmental operating junction temperature range ?40c to +105c maximum junction temperature 125c storage temperature range (ambient) ?65c to +150c stresses at or above those listed under absolute maximum ratings may cause permanent damage to the product. this is a stress rating only; functional operation of the product at these or any other conditions above those indicated in the operational section of this specification is not implied. operation beyond the maximum operating conditions for extended periods may affect product reliability. thermal characteristics thermal performance is directly linked to printed circuit board (pcb) design and operating environment. careful attention to pcb thermal design is required. table 7. thermal resistance pcb type airflow velocity (m/sec) ja jcb unit jedec 2s2p board 0.0 21.58 1, 2 1.95 1, 3 c/w 1.0 17.94 1, 2 n/a 4 c/w 2.5 16.58 1, 2 n/a 4 c/w 10-layer board 0.0 9.74 1.00 c/w 1 per jedec 51-7, plus jede c 51-5 2s2p test board. 2 per jedec jesd51-2 (still air) or jedec jesd51-6 (moving air). 3 per mil-std 883, method 1012.1. 4 n/a means not applicable. esd caution
ad6684 data sheet rev. 0 | page 12 of 107 pin configuration and fu nction descriptions 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 avdd3 vin?a vin+a avdd2 avdd2 avdd3 vin+b vin?b avdd2 avdd1 avdd1 vcm_ab dvdd dgnd drvdd2 pdwn/stby 17 fd_a 18 fd_b 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 syncinb?ab syncinb+ab drgnd drvdd1 serdoutab0? serdoutab0+ serdoutab1? serdoutab1+ serdoutcd1+ serdoutcd1? serdoutcd0+ serdoutcd0? drvdd1 syncinb+cd syncinb?cd drgnd 35 fd_d 36 fd_c 54 53 52 51 50 49 48 47 46 45 44 43 42 41 40 39 38 37 avdd3 vin?c vin+c avdd2 avdd2 avdd3 vin+d vin?d avdd2 avdd1 avdd1 vcm_cd/vref dvdd dgnd spivdd csb sclk sdio 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 notes 1. exposed pad. analog ground. the exposed thermal pad on the bottom of the p ackage provides the ground reference for avddx, spivdd, dvdd, drvdd1, and drvdd2. this exposed pad must be connected to ground for proper operation. 14994-005 ad6684 top view (not to scale) avdd2 avdd1 avdd1 avdd1 avdd1 agnd_sr sysref? sysref+ avdd1_sr agnd_sr avdd1 clk? clk+ avdd1 avdd1 avdd1 avdd1 avdd2 figure 5. pin configuration (top view) table 8. pin function descriptions pin no. mnemonic type description 0 agnd/epad ground exposed pad. analog ground. the exposed thermal pad on the bottom of the package provides the ground reference for avddx, spivdd, dvdd, drvdd1, and drvdd2. this exposed pad must be connected to ground for proper operation. 1, 6, 49, 54 avdd3 supply analog power supply (2.5 v nominal). 2, 3 vin?a, vin+a input adc a analog input complement/true. 4, 5, 9, 46, 50, 51, 55, 72 avdd2 supply analog power supply (1.8 v nominal). 7, 8 vin+b, vin?b input adc b analog input true/complement. 10, 11, 44, 45, 56, 57, 58, 59, 62, 68, 69, 70, 71 avdd1 supply analog power supply (0.975 v nominal). 12 vcm_ab output common-mode level bias output for analog input channel a and channel b 13, 42 dvdd supply digital power supply (0.975 v nominal). 14, 41 dgnd ground ground reference for dvdd and spivdd. 15 drvdd2 supply digital power supply for jesd204b pll (1.8 v nominal). 16 pdwn/stby input power-down input (active high). the operation of this pin depends on the spi mode and can be configured as power- down or standby. requires external 10 k pull-down resistor. 17, 18, 36, 35 fd_a, fd_b, fd_c, fd_d output fast detect outputs for channel a, channel b, channel c, and channel d. 19 syncinb?ab input active low jesd204b lvds sync input complement for channel a and channel b. 20 syncinb+ab input active low jesd204b lvds/cmos sync input true for channel a and channel b. 21, 32 drgnd ground ground reference for drvdd1 and drvdd2. 22, 31 drvdd1 supply digital power supply for serdout pins (0.975 v nominal).
data sheet ad6684 rev. 0 | page 13 of 107 pin no. mnemonic type description 23, 24 serdoutab0?, serdoutab0+ output lane 0 output data complement/true for channel a and channel b. 25, 26 serdoutab1?, serdoutab1+ output lane 1 output data complement/true for channel a and channel b. 27, 28 serdoutcd1+, serdoutcd1? output lane 1 output data true/complement for channel c and channel d. 29, 30 serdoutcd0+, serdoutcd0? output lane 0 output data true/complement for channel c and channel d. 33 syncinb+cd input active low jesd204b lvds/cmos sync input true for channel c and channel d. 34 syncinb?cd input active low jesd204b lvds sync input complement for channel c and channel d. 37 sdio input/output spi se rial data input/output. 38 sclk input spi serial clock. 39 csb input spi chip select (active low). 40 spivdd supply digital power supply for spi (1.8 v nominal). 43 vcm_cd/vref output/input common-mode level bias output for analog input channel c and channel d/0.5 v reference voltage input. this pin is configurable through the spi as an output or an input. use this pin as the common-mode le vel bias output if using the internal reference. this pin requires a 0.5 v reference voltage input if using an external voltage reference source. 47, 48 vin?d, vin+d input adc d analog input complement/true. 52, 53 vin+c, vin?c input adc c analog input true/complement. 60, 61 clk+, clk? input clock input true/complement. 63, 67 agnd_sr ground ground reference for sysref. 64 avdd1_sr supply analog power supply for sysref (0.975 v nominal). 65, 66 sysref+, sysref? input active low jesd204b lvds system reference (sysref) input true/complement. dc-coupled input only.
ad6684 data sheet rev. 0 | page 14 of 107 typical performance characteristics avdd1 = 0.975 v, avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, drvdd2 = 1.8 v, spivdd = 1.8 v, specified maximum sampling rate, clock divider = 4, 1.5 v p-p full-scale differential input, a in = ?1.0 dbfs, default spi settings, vdr mode (input mask not triggered), unless otherwise noted. minimum and maximum specifications are guaranteed for t he full operating junction temperature (t j ) range of ?40c to +105c. typical specifications represent performance at t j = 50c (t a = 25c). ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 67.10db sfdr = 90dbfs enob = 10.8 bits 14994-100 figure 6. single-tone fft with f in = 10.3 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 67.0db sfdr = 85dbfs enob = 10.8 bits 14994-101 figure 7. single-tone fft with f in = 155 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 66.8db sfdr = 82dbfs enob = 10.7 bits 14994-102 figure 8. single-tone fft with f in = 305 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 66.6db sfdr = 83dbfs enob = 10.7 bits 14994-103 figure 9. single-tone fft with f in = 453 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 66.5db sfdr = 75dbfs enob = 10.6 bits 14994-104 figure 10. single-tone fft with f in = 765 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 050100 frequency (mhz) amplitude (dbfs) 150 200 250 a in = ?1dbfs snr = 66.0db sfdr = 79dbfs enob = 10.6 bits 14994-105 figure 11. single-tone fft with f in = 985 mhz
data sheet ad6684 rev. 0 | page 15 of 107 60 65 70 75 80 85 90 175 200 225 250 275 300 325 350 375 400 425 450 475 500 525 550 575 600 625 650 sample rate (mhz) snr/sfdr (dbfs) sfdr snr 14994-106 figure 12. snr/sfdr vs. sample rate (f s ), f in = 155 mhz 60 65 70 snr/sfdr (dbfs) 75 analog input frequency (mhz) 80 85 95 90 10 65 85 105 125 145 165 185 205 225 245 265 365 465 565 14994-107 sfdr (dbfs), ?40c sfdr (dbfs), +105c sfdr (dbfs), +50c snrfs, ?40c snrfs, +105c snrfs, +50c figure 13. snr/sfdr vs. analog input frequency (f in ) 66.0 66.1 66.2 66.3 analog input frequency (mhz) snr (dbfs) 66.4 66.5 66.6 66.7 66.8 66.9 67.0 67.1 67.2 67.3 67.4 67.5 10 65 85 105 125 145 165 185 205 225 245 265 365 465 14994-108 figure 14. snr vs. analog input frequency (f in ), first and second nyquist zones; a in at ?3 dbfs analog input frequency (mhz) sfdr (dbfs) 10 65 85 105 125 145 165 185 205 225 245 265 365 465 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 14994-109 figure 15. sfdr vs. analog input frequency (f in ), first and second nyquist zones; a in at ?3 dbfs 465 495 525 555 585 615 645 675 705 735 765 795 66.0 analog input frequency (mhz) snr (dbfs) 66.5 67.0 67.5 14994-110 figure 16. snr vs. analog input frequency (f in ), third nyquist zone a in at ?3 dbfs 465 495 525 555 585 615 645 675 705 735 analog input frequency (mhz) sfdr (dbfs) 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 14994-111 figure 17. sfdr vs. analog input frequency (f in ), third nyquist zone; a in at ?3 dbfs
ad6684 data sheet rev. 0 | page 16 of 107 ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 0 50 100 frequency (mhz) amplitude (dbfs) 150 200 250 a in1 and a in2 = ?7dbfs sfdr = 86.4dbfs 14994-112 figure 18. two tone fft; f in1 = 153.5 mhz, f in2 = 156.5 mhz ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 0 50 100 frequency (mhz) amplitude (dbfs) 150 200 250 a in1 and a in2 = ?7dbfs sfdr = 85.9dbfs 14994-113 figure 19. two tone fft; f in1 = 303.5 mhz, f in2 = 306.5 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 ?90 ?84 ?78 ?72 ?66 ?60 ?54 ?48 analog input amplitude (dbfs) sfdr/imd3 (dbc and dbfs) ?42 ?36 ?30 ?24 ?18 ?12 0 imd3 (dbc) imd3 (dbfs) sfdr (dbfs) sfdr (dbc) 14994-114 figure 20. two tone sfdr/imd3 vs. analog input amplitude (a in ) with f in1 = 303.5 mhz and f in2 = 306.5 mhz ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 100 110 120 ?100 ?90 ?80 ?70 ?60 ?50 analog input frequency (mhz) ?40 ?30 ?20 ?10 0 sfdr (dbfs) snrfs sfdr (dbc) snr snr/sfdr (db) 14994-115 figure 21. snr/sfdr vs. analog input frequency, f in = 155 mhz ?40 ?30 ?20 ?10 0 10 20 30 40 50 60 70 80 90 100 110 120 ?100 ?90 ?80 ?70 ?60 ?50 analog input frequency (mhz) ?40 ?30 ?20 ?10 0 sfdr (dbfs) snrfs sfdr (dbc) snr snr/sfdr (db) 14994-116 figure 22. snr/sfdr vs. analog input frequency, f in = 305 mhz 60 65 70 75 snr/sfrdr (dbfs) 80 85 90 junction temperature (c) ?54 ?31 ?10 11 31 51 71 91 111 122 129 sfdr snr 14994-117 figure 23. snr/sfdr vs. junction temperature, f in = 155 mhz
data sheet ad6684 rev. 0 | page 17 of 107 ?2.0 ?1.5 ?1.0 ?0.5 0 0.5 1.0 1.5 2.0 inl (lsb) 0 1024 2048 3072 4096 5120 6144 7168 8192 output code 9216 10240 11264 12288 13312 14336 15360 16384 14994-118 figure 24. inl, f in = 10.3 mhz ?1.0 ?0.8 ?0.6 ?0.4 ?0.2 0 0.2 0.4 dnl (lsb) 0.6 0.8 1.0 0 1024 2048 3072 4096 5120 6144 7168 8192 output code 9216 10240 11264 12288 13312 14336 15360 16384 14994-119 figure 25. dnl, f in = 10.3 mhz number of hits code 6000 5000 4000 3000 2000 1000 0 n ? 10 n ? 9 n ? 8 n ? 7 n ? 6 n ? 5 n ? 4 n ? 3 n ? 2 n ? 1 0 n + 1 n + 2 n + 3 n + 4 n + 5 n + 6 n + 7 n + 8 n + 9 n + 10 14994-120 figure 26. input-referred noise histogram 1.5 1.6 temperature (c) 1.7 1.9 power dissipation (w) 2.1 1.8 2.0 14994-121 ?38 ?21 8 20 43 49 59 81 100 115 figure 27. nsr mode power dissipation vs. junction temperature 1.40 1.45 1.50 1.55 1.60 1.65 power dissipation (w) 1.70 1.75 1.80 1.85 250 300 350 400 450 sample rate (msps) 500 550 600 650 14994-122 nsr figure 28. power dissipati on vs. sample rate (f s ) ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 ?125 ?75 ?25 25 75 125 frequency (mhz) amplitude (dbfs) a in = ?1dbfs snrfs = 65.94db sfdr = 89.01dbfs 14994-123 figure 29. ddc mode (4 ddcs, dcm2, l, m, and f = 244) with f in = 305 mhz
ad6684 data sheet rev. 0 | page 18 of 107 ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 frequency (mhz) amplitude (dbfs) a in = ?1dbfs snrfs = 71.80db sfdr = 98.27dbfs ?62.5 62.5 ?42.5 ?22.5 0 17.5 37.5 57.5 14994-124 figure 30. ddc mode (4 ddcs, decimate by 4, l, m, and f = 148) with f in = 305 mhz ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 frequency (mhz) amplitude (dbfs) a in = ?1dbfs snrfs = 71.80db sfdr = 98.27dbfs ?31.25 ?21.25 ?11.25 ?1.25 8.75 18.75 28.75 14994-125 figure 31. ddc mode (4 ddcs, decimate by 8, l, m, and f = 148) with f in = 305 mhz ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 frequency (mhz) amplitude (dbfs) a in = ?1dbfs snrfs = 74.50db sfdr = 100.68dbfs ?15.625 ?10.625 ?5.625 ?0.625 4.375 9.375 14.375 14994-126 figure 32. ddc mode (4 ddcs, decimate by 16, l, m, and f = 148) with f in = 305 mhz ?160 ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 frequency (mhz) amplitude (dbfs) a in = ?1dbfs snrfs = 74.50db sfdr = 100.68dbfs 14994-127 5 25456585105125 figure 33. nsr mode (decimate by 2, l, m, and f = 124) with f in = 305 mhz ?140 ?120 ?100 ?80 ?60 ?40 ?20 0 0 25 50 75 100 125 150 175 200 225 250 amplitude (dbfs) frequency (mhz) 14994-128 a in = ?1dbfs snrfs = 70.7db sfdr = 82dbfs figure 34. nsr mode (lmf = 222) with f in = 305 mhz 65.5 65.6 65.7 65.8 65.9 66.0 66.1 66.2 66.3 66.4 66.5 66.6 66.7 66.8 66.9 67.0 0.118 0.132 0.148 0.166 0.185 0.207 0.234 0.262 0.293 0.328 0.370 0.416 differential voltage (v) 0.468 0.526 0.587 0.693 0.778 0.873 0.979 1.091 1.209 1.322 1.482 1.653 1.833 snr (dbfs) 14994-129 figure 35. snr vs. clock amplitude (differential voltage), f in = 155.3 mhz
data sheet ad6684 rev. 0 | page 19 of 107 ? 95 ?94 ?93 ?92 ?91 ?90 ?89 ?88 ?87 ?86 ?85 ?84 ?83 ?82 ?81 ?80 ?79 ?78 ?77 ?76 ?75 10 65 85 105 125 145 165 analog input frequency (mhz) sfdr (dbfs) 185 205 225 245 265 365 465 buffer current = 160a buffer current = 200a buffer current = 240a buffer current = 280a 14994-130 figure 36. sfdr vs. analog input frequency with different buffer current settings (first and second nyquist zones) ? 85 ?84 ?83 ?82 ?81 ?80 ?79 ?78 ?77 ?76 ?75 ?74 ?73 ?72 ?71 ?70 ?69 ?68 ?67 ?66 ?65 465 495 525 555 585 615 645 675 705 735 analog input frequency (mhz) sfdr (dbfs) buffer current = 200a buffer current = 240a buffer current = 280a buffer current = 320a 14994-131 figure 37. sfdr vs. analog input frequency with different buffer current settings (third nyquist zone) ? 80 ?78 ?76 ?74 ?72 ?70 ?68 ?66 ?64 ?62 ?60 ?58 ?56 ?54 ?52 ?50 ?48 ?46 ?44 ?42 ?40 analog input frequency (mhz) sfdr (dbfs) 730 760 790 820 850 880 910 940 970 1030 1060 1090 1120 1150 1180 1210 1240 1270 1300 1330 1360 1390 1420 1450 1480 1510 1540 1570 1600 1630 1660 1690 1720 1750 1780 1810 buffer current = 320a buffer current = 360a buffer current = 400a buffer current = 440a 14994-132 figure 38. sfdr vs. analog input frequency with different buffer current settings (fourth nyquist zone) analog input frequency (mhz) 64 65 66 67 68 69 10 65 85 105 125 snr (dbfs) 145 165 185 205 225 245 265 365 465 input full scale = 2.16v input full scale = 1.44v 14994-133 figure 39. snr vs. analog input frequency with different analog input full scales (first and second nyquist zones) input full scale = 2.16v input full scale = 1.44v 465.3 495.3 525.3 555.3 585.3 615.3 645.3 675.3 705.3 735.3 analog input frequency (mhz) 64.0 64.2 64.4 64.6 64.8 65.0 65.2 65.4 65.6 65.8 66.0 66.2 66.4 66.6 66.8 67.0 67.2 67.4 67.6 67.8 68.0 68.2 68.4 68.6 68.8 69.0 snr (dbfs) 14994-134 figure 40. snr vs. analog input frequency with different analog input full scales (third nyquist zone) 62 63 64 65 66 67 68 730 760 790 820 850 880 910 940 970 1000 1030 1060 1090 1120 1150 1180 1210 1240 1270 1300 1330 1360 1390 1420 1450 1480 1510 1540 1570 1600 1630 1660 1690 1720 1750 1780 1810 input full scale = 2.16v input full scale = 1.44v analog input frequency (mhz) snr (dbfs) 14994-135 figure 41. snr vs. analog input frequency with different analog input full scales (fourth nyquist zone)
ad6684 data sheet rev. 0 | page 20 of 107 ? 90 ?89 ?88 ?87 ?86 ?85 ?84 ?83 ?82 ?81 ?80 ?79 ?78 ?77 ?76 ?75 ?74 ?73 ?72 ?71 ?70 10 65 85 105 125 145 165 185 205 225 245 265 365 465 565 input full scale = 2.16v input full scale = 1.44v analog input frequency (mhz) sfdr (dbfs) 14994-136 figure 42. sfdr vs. analog input frequency with different analog input full scales (first and second nyquist zones) ? 90 ?89 ?88 ?87 ?86 ?85 ?84 ?83 ?82 ?81 ?80 ?79 ?78 ?77 ?76 ?75 ?74 ?73 ?72 ?71 ?70 465 495 525 555 585 615 645 675 705 735 765 795 input full scale = 2.16v input full scale = 1.44v analog input frequency (mhz) sfdr (dbfs) 14994-137 figure 43. sfdr vs. analog input frequency with different analog input full scales (third nyquist zone) ? 81 ?79 ?77 ?75 ?73 ?71 ?69 ?67 ?65 ?63 ?61 ?59 ?57 ?55 730 790 850 910 970 1060 1120 1180 1240 1300 1360 1420 1480 1540 1600 1660 1720 1780 analog input frequency (mhz) sfdr (dbfs) input full scale = 2.16v input full scale = 1.44v 14994-138 figure 44. sfdr vs. analog input frequency with different analog input full scales (fourth nyquist zone)
data sheet ad6684 rev. 0 | page 21 of 107 equivalent circuits a in control (spi) 10pf vin+x 100 ? vin?x avdd3 avdd3 v cm buffer 400 ? 100 ? avdd3 avdd3 3.5pf avdd3 3.5pf 14994-024 figure 45. analog inputs avdd1 25 ? avdd1 25 ? 16k ? 16k ? v cm = 0.69v clk+ clk? 14994-025 figure 46. clock inputs 130k ? 130k ? level translator sysref+ 10k ? ? ? 100 ? 14994-026 figure 47. sysref inputs drvdd drgnd drvdd drgnd output driver emphasis/swing control (spi) data+ data? serdoutabx+/ serdoutcdx+ x = 0, 1 serdoutabx?/ serdoutcdx? x = 0, 1 14994-027 figure 48. digital outputs 130k ? 130k ? level translator syncinb+ab/ syncinb+cd syncinb?ab/ syncinb?cd 10k ? 1.9pf 1.9pf 100 ? 2.5k ? 10k ? 100 ? drvdd drgnd drvdd drgnd drvdd drgnd drgnd drgnd cmos path syncinb pin control (spi) 14994-028 figure 49. syncinbab, syncinbcd inputs 56k ? dgnd dgnd spivdd esd protected esd protected spivdd sclk 14994-029 figure 50. sclk input 56k ? dgnd dgnd esd protected esd protected spivdd csb 14994-030 figure 51. csb input
ad6684 data sheet rev. 0 | page 22 of 107 56k ? spivdd sdi dgnd dgnd dgnd dgnd sdo esd protected esd protected spivdd spivdd sdio 14994-031 figure 52. sdio input fd_a/fd_b/ fd_c/fd_d fd fd_x pin control (spi) jesd204b lmfc jesd204b sync 14994-032 56k ? spivdd dgnd dgnd dgnd esd protected esd protected spivdd figure 53. fd_a/fd_b/fd_c/fd_d outputs esd protected esd protected spivdd dgnd dgnd pdwn/ stby pdwn control (spi) 14994-033 figure 54. pdwn/stby input vref pin control (spi) v ref agnd avdd2 temperature diode voltage external reference voltage input 14994-034 figure 55. vref input/output
data sheet ad6684 rev. 0 | page 23 of 107 theory of operation adc architecture the architecture of the ad6684 consists of an input buffered pipelined adc. the input buffer is designed to provide a 200 termination impedance to the analog input signal. the equivalent circuit diagram of the analog input termination is shown in figure 45. the input buffer provides a linear high input impedance (for ease of drive) and reduces kickback from the adc. the buffer is optimized for high linearity, low noise, and low power. the quantized outputs from each stage are combined into a final 14-bit result in the digital correction logic. the pipelined architecture permits the first stage to operate with a new input sample while, at the same time, the remaining stages operate with the preceding samples. sampling occurs on the rising edge of the clock. analog input considerations the analog input to the ad6684 is a differential buffer with an internal common-mode voltage of 1.34 v. the clock signal alternately switches the input circuit between sample mode and hold mode. either a differential capacitor or two single-ended capacitors can be placed on the inputs to provide a matching passive network. this configuration ultimately creates a low-pass filter at the input, which limits unwanted broadband noise. see figure 57 and figure 58 for details on input network recom- mendations. for more information, see the analog dialogue article transformer-coupled front-end for wideband a/d converters (volume 39, april 2005). in general, the precise values depend on the application. for best dynamic performance, the source impedances driving vin+x and vin?x must be matched such that common-mode settling errors are symmetrical. these errors are reduced by the common-mode rejection of the adc. an internal reference buffer creates a differential reference that defines the span of the adc core. maximum snr performance is achieved by setting the adc to the largest span in a differential configuration. in the case of the ad6684 , the available span is programmable through the spi port from 1.44 v p-p to 2.16 v p-p differential with 1.80 v p-p differential being the default. dither the ad6684 has internal on-chip dither circuitry that improves the adc linearity and sfdr, particularly at smaller signal levels. a known but random amount of white noise is injected into the input of the ad6684 . this dither improves the small signal linearity within the adc transfer function and is precisely subtracted out digitally. the dither is turned on by default and does not reduce the adc input dynamic range. the data sheet specifications and limits are obtained with the dither turned on. the dither can be disabled using spi writes to register 0x0922. disabling the dither can slightly improve the snr (by about 0.2 db) at the expense of the small signal sfdr. differential input configurations there are several ways to drive the ad6684 , either actively or passively. however, optimum performance is achieved by driving the analog input differentially. for applications where snr and sfdr are key parameters, differential transformer coupling is the recommended input configuration (see figure 57 and figure 58) because the noise performance of most amplifiers is not adequate to achieve the true performance of the ad6684 . for low to midrange frequencies, a double balun or double transformer network (see figure 57) is recommended for optimum performance of the ad6684 . for higher frequencies in the second or third nyquist zones, it is recommended to remove some of the front-end passive components to ensure wideband operation (see figure 58). input common mode the analog inputs of the ad6684 are internally biased to the common mode as shown in figure 56. for dc-coupled applications, the recommended operation procedure is to export the common-mode voltage to the vcm_cd/vref pin using the spi writes listed in this section. the common-mode voltage must be set by the exported value to ensure proper adc operation. disconnect the internal common-mode buffer from the analog input using register 0x1908. when performing spi writes for dc coupling operation, use the following register settings in order: 1. set register 0x1908, bit 2 to 1; this setting disconnects the internal common-mode buffer from the analog input. 2. set register 0x18a6 to 0x00; this setting turns off the voltage reference. 3. set register 0x18e6 to 0x00; this setting turns off the temperature diode export. 4. set register 0x18e0 to 0x04. 5. set register 0x18e1 to 0x1c. 6. set register 0x18e2 to 0x14. 7. set register 0x18e3, bit 6 to 0x01; this setting turns on the vcm export. 8. set register 0x18e3, bits[5:0] to the buffer current setting (copy the buffer current setting from register 0x1a4c and register 0x1a4d to improve the accuracy of the common- mode export).
ad6684 data sheet rev. 0 | page 24 of 107 analog input controls and sfdr optimization the ad6684 offers flexible controls for the analog inputs, such as buffer current and input full-scale adjustment. all of the available controls are shown in figure 56. a in control (spi) 10pf vin+x 100 ? vin?x avdd3 avdd3 v cm buffer 400 ? 100 ? avdd3 avdd3 3.5pf avdd3 3.5pf 14994-037 figure 56. analog input controls using register 0x1a4c and register 0x1a4d, the buffer currents on each channel can be scaled to optimize the sfdr over various input frequencies and bandwidths of interest. as the input buffer currents are set, the amount of current required by the avdd3 supply changes. this relationship is shown in figure 59. for a complete list of buffer current settings, see table 46. 10 ? 0.1f vin+x vin?x 0.1f 0.1f balun 50 ? agnd agnd agnd 10 ? 50 ? 10 ? 10 ? 0 ? 2pf 2pf 2pf 10 ? 10 ? 0 ? 14994-038 figure 57. differential transformer coupled configuration for first and second nyquist frequencies 10? 0.1f vin+x vin?x 0.1f 0.1f 50 ? agnd agnd agnd dni 50 ? dni 10? 0 ? dni dni dni 10? 10? 0 ? 14994-039 balun figure 58. differential transformer coupled configuration for third and fourth nyquist zones
data sheet ad6684 rev. 0 | page 25 of 107 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 100 150 200 250 300 350 400 450 500 550 600 buffer current setting (a) avdd3 power (w) 14994-139 figure 59. avdd3 power vs. buffer current setting in certain high frequency applications, the sfdr can be improved by reducing the full-scale setting. table 9 shows the recommended buffer current settings for the different analog input frequency ranges. table 9. sfdr optimization for input frequencies nyquist one input buffer current control setting, register 0x1a4c and register 0x1a4d first, second, and third nyquist 240 (register 0x1a4c, bits[5:0] = register 0x1a4d, bits[5:0] = 01100) fourth nyquist 400 (register 0x1a4c, bits[5:0] = register 0x1a4d, bits[5:0] = 10100) absolute maximum input swing the absolute maximum input swing allowed at the inputs of the ad6684 is 4.3 v p-p differential. signals operating near or at this level can cause permanent damage to the adc. voltage reference a stable and accurate 0.5 v voltage reference is built into the ad6684 . this internal 0.5 v reference is used to set the full- scale input range of the adc. the full-scale input range can be adjusted via the adc function register (register 0x1910). for more information on adjusting the input swing, see table 46. figure 60 shows the block diagram of the internal 0.5 v reference controls. adc core full-scale voltage adjust vref pin control spi register (0x18a6) vref vin?a/ vin?b v in+a/ vin+b internal vref generator input full-scale range adjust spi register (0x1910) 14994-040 figure 60. internal reference configuration and controls the spi register 0x18a6 enables the user to either use this internal 0.5 v reference, or to provide an external 0.5 v reference. when using an external voltage reference, provide a 0.5 v reference. the full-scale adjustment is made using the spi, irrespective of the reference voltage. for more information on adjusting the full-scale level of the ad6684 , refer to the memory map section. the spi writes required to use the external voltage reference, in order, are as follows: 1. set register 0x18e3 to 0x00 to turn off vcm export. 2. set register 0x18e6 to 0x00 to turn off temperature diode export. 3. set register 0x18a6 to 0x01 to turn on the external voltage reference. the use of an external reference may be necessary, in some applications, to enhance the gain accuracy of the adc or to improve thermal drift characteristics. the external reference has to be a stable 0.5 v reference. the adr130 is a good option for providing the 0.5 v reference. figure 61 shows how the adr130 can be used to provide the external 0.5 v reference to the ad6684 . the grayed out areas show unused blocks within the ad6684 while using the adr130 to provide the external reference. full-scale voltage adjust vref 0.1f v out 4 set 5 nc 6 v in 3 gnd 2 nc 1 adr130 0.1f input vref pin and full-scale voltage control internal vref generator 14994-042 figure 61. external reference using adr130
ad6684 data sheet rev. 0 | page 26 of 107 clock input considerations for optimum performance, drive the ad6684 sample clock inputs (clk+ and clk?) with a differential signal. this signal is typically ac-coupled to the clk+ and clk? pins via a transformer or clock drivers. these pins are biased internally and require no additional biasing. figure 62 shows a preferred method for clocking the ad6684 . the low jitter clock source is converted from a single-ended signal to a differential signal using an rf transformer. adc clk+ clk? 0.1f 0.1f 100 ? 50 ? c lock input 1:1z 14994-043 figure 62. transformer-coupled differential clock another option is to ac couple a differential cml or lvds signal to the sample clock input pins, as shown in figure 63 and figure 64. adc clk+ clk? 0.1f 0.1f z0 = 50 ? z0 = 50 ? 33? 33? 71? 10pf 3.3v 14994-044 figure 63. differential cml sample clock adc clk+ clk? 0.1f 0.1f 0.1f 0.1f 50? 1 50 ? 1 100 ? clock input lvds driver clk+ clk? 1 50 ? resistors are optional. clock input 14994-045 figure 64. differential lvds sample clock clock duty cycle considerations typical high speed adcs use both clock edges to generate a variety of internal timing signals. the ad6684 contains an internal clock divider and a duty cycle stabilizer (dcs). in applications where the clock duty cycle cannot be guaranteed to be 50%, a higher multiple frequency clock along with the usage of the clock divider is recommended. when it is not possible to provide a higher frequency clock, it is recommended to turn on the dcs using register 0x011c. the output of the divider offers a 50% duty cycle, high slew rate (fast edge) clock signal to the internal adc. see the memory map section for more details on using this feature. input clock divider the ad6684 contains an input clock divider with the ability to divide the input clock by 1, 2, 4, and 8. the divider ratios can be selected using register 0x0108 (see figure 65). in applications where the clock input is a multiple of the sample clock, care must be taken to program the appropriate divider ratio into the clock divider before applying the clock signal. this ratio ensures that the current transients during device startup are controlled. clk+ clk? 2 4 reg 0x0108 8 14994-046 figure 65. clock divider circuit the ad6684 clock divider can be synchronized using the external sysref input. a valid sysref causes the clock divider to reset to a programmable state. this synchronization feature allows multiple devices to have their clock dividers aligned to guarantee simultaneous input sampling. clock jitter considerations high speed, high resolution adcs are sensitive to the quality of the clock input. the degradation in snr at a given input frequency (f a ) due only to aperture jitter (t j ) can be calculated by snr = ?20 log (2 f a t j ) in this equation, the rms aperture jitter represents the root mean square of all jitter sources, including the clock input, analog input signal, and adc aperture jitter specifications. if undersampling applications are particularly sensitive to jitter (see figure 66). 14994-047 130 120 110 100 90 80 70 60 50 40 30 10 100 1000 10000 snr (db) analog input frequency (mhz) 12.5 f s 25 f s 50 f s 100 f s 200 f s 400 f s 800 f s figure 66. ideal snr vs. analog input frequency and jitter
data sheet ad6684 rev. 0 | page 27 of 107 treat the clock input as an analog signal in cases where aperture jitter may affect the dynamic range of the ad6684 . separate the power supplies for clock drivers from the adc output driver supplies to avoid modulating the clock signal with digital noise. if the clock is generated from another type of source (by gating, dividing, or other methods), retime the clock by the original clock at the last step. refer to the an-501 application note and the an-756 application note for more in-depth information about jitter performance as it relates to adcs. figure 66 shows the estimated snr of the ad6684 across input frequency for different clock induced jitter values. the snr can be estimated by using the following equation: ? ? ? ? ? ? ? ? ? ? ? ?? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 10 10 10 1010log (dbfs) jitter adc snr snr snr power-down/standby mode the ad6684 has a pdwn/stby pin that can be used to configure the device in power-down or standby mode. the default operation is power-down. the pdwn/stby pin is a logic high pin. when in power-down mode, the jesd204b link is disrupted. the power-down option can also be set via register 0x003f and register 0x0040. in standby mode, the jesd204b link is not disrupted and transmits zeros for all converter samples. this setting can be changed using register 0x0571, bit 7 to select /k/ characters. temperature diode the ad6684 contains a diode-based temperature sensor for measuring the temperature of the die. the diode can output a voltage and serve as a coarse temperature sensor to monitor the internal die temperature. the temperature diode voltage can be output to the vcm_cd/ vref pin using the spi. use register 0x18e6 to enable or disable the diode. register 0x18e6 is a local register. both cores must be selected in the core index register (register 0x0009 = 0x03) to enable the temperature diode readout. it is important to note that other voltages may be exported to the same pin at the same time, which may result in undefined behavior. thus, to ensure a proper readout, switch off all other voltage exporting circuits as detailed in this section. the spi writes required to export the temperature diode are as follows (see table 46 for more information): 1. set register 0x0009 to 0x03 to select both cores. 2. set register 0x18e3 to 0x00 to turn off vcm export. 3. set register 0x18a6 to 0x00 to turn off the voltage reference. 4. set register 0x18e6 to 0x01 to turn on temperature diode export. the typical voltage response of the temperature diode is shown in figure 67. however, it is recommended to take measurements from a pair of diodes into account when introducing another step. 5. set register 0x18e6 to 0x02 to turn on the second temperature diode (that is, 20 the size) of the pair. for the method utilizing two diodes simultaneously giving a more accurate result, see the an-1432 application note , practical thermal modeling and measurements in high power ics. 0.80 0.75 0.70 0.65 0.60 0.55 0.50 ?40 ?20 0 20 junction temperature (c) temper a ture diode voltage (v) 40 60 80 100 14994-048 figure 67. temperature diode voltage vs. junction temperature
ad6684 data sheet rev. 0 | page 28 of 107 adc overrange and fast detect in receiver applications, it is desirable to have a mechanism to reliably determine when the converter is about to be clipped. the standard overrange bit in the jesd204b outputs provides information on the state of the analog input that is of limited usefulness. therefore, it is helpful to have a programmable threshold below full scale that allows time to reduce the gain before the clip actually occurs. in addition, because input signals can have significant slew rates, the latency of this function is of major concern. highly pipelined converters can have significant latency. the ad6684 contains fast detect circuitry for individual channels to monitor the threshold and to assert the fd_a, fd_b, fd_c, and fd_d pins. adc overrange the adc overrange indicator is asserted when an overrange is detected on the input of the adc. the overrange indicator can be embedded within the jesd204b link as a control bit. the latency of this overrange indicator matches the sample latency. fast threshold detectio n (fd_a, fd_b, fd_c and fd_d) the fd bits (register 0x0040, bits[5:0]) are immediately set whenever the absolute value of the input signal exceeds the programmable upper threshold level. the fd bits are only cleared when the absolute value of the input signal drops below the lower threshold level for greater than the programmable dwell time. this feature provides hysteresis and prevents the fd bits from excessively toggling. the operation of the upper threshold and lower threshold registers, along with the dwell time registers, is shown in figure 68. the fd indicator is asserted if the input magnitude exceeds the value programmed in the fast detect upper threshold registers, located at register 0x0247 and register 0x0248. the selected threshold register is compared with the signal magnitude at the output of the adc. the fast upper threshold detection has a latency of 30 clock cycles (maximum). the approximate upper threshold magnitude is defined by upper threshold magnitude (dbfs) = 20log ( threshold magnitude /2 13 ) the fd indicators are not cleared until the signal drops below the lower threshold for the programmed dwell time. the lower threshold is programmed in the fast detect lower threshold registers, located at register 0x0249 and register 0x024a. the fast detect lower threshold register is a 13-bit register that is compared with the signal magnitude at the output of the adc. this comparison is subject to the adc pipeline latency, but is accurate in terms of converter resolution. the lower threshold magnitude is defined by lower threshold magnitude (dbfs) = 20log ( threshold magnitude /2 13 ) for example, to set an upper threshold of ?6 dbfs, write 0xfff to register 0x0247 and register 0x0248. to set a lower threshold of ?10 dbfs, write 0xa1d to register 0x0249 and register 0x024a. the dwell time can be programmed from 1 to 65,535 sample clock cycles by placing the desired value in the fast detect dwell time registers, located at register 0x024b and register 0x024c. see the memory map section (register 0x040, and register 0x245 to register 0x24c in table 45) for more details. upper threshold lower threshold fd_a or fd_b midscale dwell time timer reset by rise above lower threshold timer completes before signal rises above lower threshold dwell time 14994-050 figure 68. threshold settings for the fd_a and fd_b signals
data sheet ad6684 rev. 0 | page 29 of 107 signal monitor the signal monitor block provides additional information about the signal being digitized by the adc. the signal monitor computes the peak magnitude of the digitized signal. this information can be used to drive an agc loop to optimize the range of the adc in the presence of real-world signals. the results of the signal monitor block can be obtained either by reading back the internal values from the spi port or by embedding the signal monitoring information into the jesd204b interface as special control bits. a global, 24-bit programmable period controls the duration of the measurement. figure 69 shows the simplified block diagram of the signal monitor block. from memory map down counter is count = 1? magnitude storage register from input signal monitor holding register load clear compare a > b load load to sport over jesd204b and memory map signal monitor period register (smpr) 0x0271, 0x0272, 0x0273 14994-051 figure 69. signal monitor block the peak detector captures the largest signal within the observation period. the detector only observes the magnitude of the signal. the resolution of the peak detector is a 13-bit value, and the observation period is 24 bits and represents converter output samples. the peak magnitude can be derived by using the following equation: peak magnitude (dbfs) = 20log( peak detector value /2 13 ) the magnitude of the input port signal is monitored over a programmable time period, which is determined by the signal monitor period register (smpr). the peak detector function is enabled by setting bit 1 of register 0x0270 in the signal monitor control register. the 24-bit smpr must be programmed before activating this mode. after enabling peak detection mode, the value in the smpr is loaded into a monitor period timer, which decrements at the decimated clock rate. the magnitude of the input signal is compared with the value in the internal magnitude storage register (not accessible to the user), and the greater of the two is updated as the current peak level. the initial value of the magnitude storage register is set to the current adc input signal magnitude. this comparison continues until the monitor period timer reaches a count of 1. when the monitor period timer reaches a count of 1, the 13-bit peak level value is transferred to the signal monitor holding register, which can be read through the memory map or output through the sport over the jesd204b interface. the monitor period timer is reloaded with the value in the smpr, and the countdown restarts. in addition, the magnitude of the first input sample is updated in the magnitude storage register, and the comparison and update procedure, as explained previously, continues. sport over jesd204b the signal monitor data can also be serialized and sent over the jesd204b interface as control bits. these control bits must be deserialized from the samples to reconstruct the statistical data. the signal control monitor function is enabled by setting bits[1:0] of register 0x0279 and bit 1 of register 0x027a. figure 70 shows two different example configurations for the signal monitor control bit locations inside the jesd204b samples. a maximum of three control bits can be inserted into the jesd204b samples; however, only one control bit is required for the signal monitor. control bits are inserted from msb to lsb. if only one control bit is to be inserted (cs = 1), only the most significant control bit is used (see example configuration 1 and example configuration 2 in figure 70). to select the sport over jesd204b option, program register 0x0559, register 0x055a, and register 0x058f. see table 46 for more information on setting these bits. figure 71 shows the 25-bit frame data that encapsulates the peak detector value. the frame data is transmitted msb first with five 5-bit subframes. each subframe contains a start bit that can be used by a receiver to validate the deserialized data. figure 72 shows the sport over jesd204b signal monitor data with a monitor period timer set to 80 samples.
ad6684 data sheet rev. 0 | page 30 of 107 15 14-bit converter resolution (n = 14) tail x 1 control bit (cs = 1) 1-bit control bit (cs = 1) 14131211109876543210 1514131211109876543210 1 tail bit serialized signal monitor frame data example configuration 1 (n' = 16, n = 15, cs = 1) example configuration 2 (n' = 16, n = 14, cs = 1) serialized signal monitor frame data 16-bit jesd204b sample size (n' = 16) s[13] x s[12] x s[11] x s[10] x s[9] x s[8] x s[7] x s[6] x s[5] x s[4] x s[3] x s[2] x s[1] x s[0] x ctrl [bit 2] x ctrl [bit 2] x s[14] x s[13] x s[12] x s[11] x s[10] x s[9] x s[8] x s[7] x s[6] x s[5] x s[4] x s[3] x s[2] x s[1] x s[0] x 15-bit converter resolution (n = 15) 16-bit jesd204b sample size (n' = 16) 14994-052 figure 70. signal monito r control bit locations 25-bit frame 5-bit idle subframe (optional) 5-bit identifier subframe 5-bit data msb subframe 5-bit data subframe 5-bit data subframe 5-bit data lsb subframe 5-bit subframes p[ ] = peak magnitude value idle 1 idle 1 idle 1 idle 1 idle 1 start 0 p[0]000 start 0 p[4] p[3] p[2] p[1] start 0 p[8] p[7] p[6] p5] start 0 p[12] p[11] p[10] p[9] start 0 id[3] 0 id[2] 0 id[1] 0 id[0] 1 14994-053 figure 71. sport over jesd204b signal monitor frame data
data sheet ad6684 rev. 0 | page 31 of 107 payload 3 25-bit frame (n) payload 3 25-bit frame (n + 1) payload 3 25-bit frame (n + 2) idle idle idle idle idle idle idle idle idle idle idle data msb data data data lsb idle idle idle idle idle idle idle idle idle idle idle ident- ifier ident- ifier ident- ifier data msb data data data lsb idle idle idle idle idle idle idle idle idle idle idle data msb data data data lsb smpr = 80 samples (0x0271 = 0x50; 0x0272 = 0x00; 0x0273 = 0x00) 80 sample period 80 sample period 80 sample period 14994-054 figure 72. sport over jesd204b signal monitor example with period = 80 samples
ad6684 data sheet rev. 0 | page 32 of 107 digital downconverter (ddc) the ad6684 includes four ddcs that provide filtering and reduce the output data rate. this digital processing section includes an nco, a half-band decimating filter, a finite impulse response (fir) filter, a gain stage, and a complex to real conversion stage. each of these processing blocks has control lines that allow it to be independently enabled and disabled to provide the desired processing function. each pair of adc channels has two ddcs (ddc0 and ddc1) for a total of four ddcs. the digital down- converter can be configured to output either real data or complex output data. the ddcs output a 16-bit stream. to enable this operation, the converter number of bits, n, is set to a default value of 16, even though the analog core only outputs 14 bits. in full bandwidth operation, the adc outputs are 9-bit words followed by seven zeros, unless the tail bits are enabled. ddc i/q input selection the ad6684 has four adc channels and four ddc channels. each ddc channel has two input ports that can be paired to support both real and complex inputs through the i/q crossbar mux. for real signals, both ddc input ports must select the same adc channel (that is, ddc input port i = adc channel a and ddc input port q = adc channel a). for complex signals, each ddc input port must select different adc channels (that is, ddc input port i = adc channel a and ddc input port q = adc channel b, or ddc input port i = adc channel c and ddc input port q = adc channel d). the inputs to each ddc are controlled by the ddc input selec- tion registers (register 0x0311 and register 0x0331) in conjunction with the pair index register (register 0x0009). see table 45 and table 46 for information on how to configure the ddcs. ddc i/q output selection each ddc channel has two output ports that can be paired to support both real and complex outputs. for real output signals, only the ddc output port i is used (the ddc output port q is invalid). for complex i/q output signals, both ddc output port i and ddc output port q are used. the i/q outputs to each ddc channel are controlled by the ddc complex to real enable bit, bit 3 in the ddc control registers (register 0x0310 and register 0x0330) in conjunction with the pair index register (register 0x0009). the chip q ignore bit in the chip mode register (register 0x0200, bit 5) controls the chip output muxing of all the ddc channels. when all ddc channels use real outputs, set this bit high to ignore all ddc q output ports. when any of the ddc channels are set to use complex i/q outputs, the user must clear this bit to use both ddc output port i and ddc output port q. for more information, see figure 81. ddc general description the four ddc blocks are used to extract a portion of the full digital spectrum captured by the adc(s). the ddc blocks are intended for if sampling or oversampled baseband radios requiring wide bandwidth input signals. each ddc block contains the following signal processing stages: ? frequency translation stage (optional) ? filtering stage ? gain stage (optional) ? complex to real conversion stage (optional) frequency translation stage (optional) this stage consists of a 48-bit complex nco and quadrature mixers that can be used for frequency translation of both real and complex input signals. this stage shifts a portion of the available digital spectrum down to baseband. filtering stage after shifting down to baseband, this stage decimates the frequency spectrum using a chain of up to four half-band, low- pass filters for rate conversion. the decimation process lowers the output data rate, which in turn reduces the output interface rate. gain stage (optional) to compensate for losses associated with mixing a real input signal down to baseband, this stage adds an additional 0 db or 6 db of gain. complex to real conversion stage (optional) when real outputs are necessary, this stage converts the complex outputs back to real by performing an f s /4 mixing operation plus a filter to remove the complex component of the signal. figure 73 shows the detailed block diagram of the ddcs implemented in the ad6684.
data sheet ad6684 rev. 0 | page 33 of 107 nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 1 sysref real/i real/q real/i converter 2 q converter 3 i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 0 sysref real/i real/q real/i converter 0 q converter 1 i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 1 sysref real/i real/q real/i converter 2 q converter 3 i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 0 sysref real/i real/q real/i converter 0 q converter 1 i q i/q crossbar mux i/q crossbar mux adc sampling at f s real/i adc sampling at f s real/q adc sampling at f s real/i adc sampling at f s real/q synchronization control circuits sysref 14994-055 l jesd204b lanes at up to 15gbps l jesd204b lanes at up to 15gbps jesd204b transmit interface jesd204b transmit interface figure 73. ddc detailed block diagram figure 74 shows an example usage of one of the four ddc blocks with a real input signal and four half-band filters (hb4 + hb3 + hb2 + hb1). it shows both complex (decimate by 16) and real (decimate by 8) output options. when ddcs have different decimation ratios, the chip decimation ratio (register 0x0201) must be set to the lowest decimation ratio of all the ddc blocks on a per pair basis in conjunction with the pair index (register 0x0009). in this scenario, samples of higher decimation ratio ddcs are repeated to match the chip decimation ratio sample rate. whenever the nco frequency is set or changed, the ddc soft reset must be issued. if the ddc soft reset is not issued, the output may potentially show amplitude variations. table 10, table 11, table 12, table 13, and table 14 show the ddc samples when the chip decimation ratio is set to 1, 2, 4, 8, or 16, respectively. when ddcs have different decimation ratios, the chip decimation ratio must be set to the lowest decimation ratio of all the ddc channels in the respective channel pair (channel a/channe l b or channel c/channel d). in this scenario, samples of higher decimation ratio ddcs are repeated to match the chip decimation ratio sample rate.
ad6684 data sheet rev. 0 | page 34 of 107 cos( t) 0 90 i q real bandwidth of interest bandwidth of interest image digital filter response dc dc adc sampling at f s real real half- band filter hb4 fir 2 half- band filter hb3 fir 2 half- band filter hb2 fir 2 half- band filter hb1 fir i i half- band filter hb4 fir 2 half- band filter hb3 fir 2 half- band filter hb2 fir 2 2 2 half- band filter hb1 fir q q adc real input?sampled at f s filtering stage 4 digital half-band filters (hb4 + hb3 + hb2 + hb1) frequency translation stage (optional) digital mixer + nco for f s /3 tuning, the frequency tuning word = round (( f s /3)/ f s 2 48 ) = +9.3825 13 (0x555555555555) nco tunes center of bandwidth of interest to baseband bandwidth of interest image (?6db loss due to nco + mixer) bandwidth of interest (?6db loss due to nco + mixer) ? f s /2 ? f s /3 ? f s /4 ? f s /8 f s /16 f s /8 f s /4 f s /3 f s /2 ? f s /16 ? f s /32 f s /32 ? f s /2 ? f s /3 ? f s /4 ? f s /8 f s /16 f s /8 f s /4 f s /3 f s /2 ? f s /16 ? f s /32 f s /32 ?sin( t) 48-bit nco dc digital filter response dc dc i q i q 2 2 i q real/i complex to real i q gain stage (optional) 0db or 6db gain complex (i/q) outputs decimate by 16 gain stage (optional) 0db or 6db gain real (i) outputs decimate by 8 complex to real conversion stage (optional) f s /4 mixing + complex filter to remove q ? f s /8 f s /16 f s /8 ? f s /16 ? f s /32 f s /32 ? f s /8 f s /16 f s /8 ? f s /16 ? f s /32 f s /32 f s /16 ? f s /16 ? f s /32 f s /32 6db gain to compensate for nco + mixer loss 6db gain to compensate for nco + mixer loss downsample by 2 +6db +6db +6db +6db 14994-056 figure 74. ddc theory of operation example (real input, decimate by 16)
data sheet ad6684 rev. 0 | page 35 of 107 table 10. ddc samples in each jesd204b link when chip decimation ratio = 1 real (i) output (complex to real enabled) co mplex (i/q) outputs (complex to real disabled) hb1 fir (dcm 1 = 1) hb2 fir + hb1 fir (dcm 1 = 2) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 4) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb1 fir (dcm 1 = 2) hb2 fir + hb1 fir (dcm 1 = 4) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) n n n n n n n n n + 1 n n n n n n n n + 2 n + 1 n n n + 1 n n n n + 3 n + 1 n n n + 1 n n n n + 4 n + 2 n + 1 n n + 2 n + 1 n n n + 5 n + 2 n + 1 n n + 2 n + 1 n n n + 6 n + 3 n + 1 n n + 3 n + 1 n n n + 7 n + 3 n + 1 n n + 3 n + 1 n n n + 8 n + 4 n + 2 n + 1 n + 4 n + 2 n + 1 n n + 9 n + 4 n + 2 n + 1 n + 4 n + 2 n + 1 n n + 10 n + 5 n + 2 n + 1 n + 5 n + 2 n + 1 n n + 11 n + 5 n + 2 n + 1 n + 5 n + 2 n + 1 n n + 12 n + 6 n + 3 n + 1 n + 6 n + 3 n + 1 n n + 13 n + 6 n + 3 n + 1 n + 6 n + 3 n + 1 n n + 14 n + 7 n + 3 n + 1 n + 7 n + 3 n + 1 n n + 15 n + 7 n + 3 n + 1 n + 7 n + 3 n + 1 n n + 16 n + 8 n + 4 n + 2 n + 8 n + 4 n + 2 n + 1 n + 17 n + 8 n + 4 n + 2 n + 8 n + 4 n + 2 n + 1 n + 18 n + 9 n + 4 n + 2 n + 9 n + 4 n + 2 n + 1 n + 19 n + 9 n + 4 n + 2 n + 9 n + 4 n + 2 n + 1 n + 20 n + 10 n + 5 n + 2 n + 10 n + 5 n + 2 n + 1 n + 21 n + 10 n + 5 n + 2 n + 10 n + 5 n + 2 n + 1 n + 22 n + 11 n + 5 n + 2 n + 11 n + 5 n + 2 n + 1 n + 23 n + 11 n + 5 n + 2 n + 11 n + 5 n + 2 n + 1 n + 24 n + 12 n + 6 n + 3 n + 12 n + 6 n + 3 n + 1 n + 25 n + 12 n + 6 n + 3 n + 12 n + 6 n + 3 n + 1 n + 26 n + 13 n + 6 n + 3 n + 13 n + 6 n + 3 n + 1 n + 27 n + 13 n + 6 n + 3 n + 13 n + 6 n + 3 n + 1 n + 28 n + 14 n + 7 n + 3 n + 14 n + 7 n + 3 n + 1 n + 29 n + 14 n + 7 n + 3 n + 14 n + 7 n + 3 n + 1 n + 30 n + 15 n + 7 n + 3 n + 15 n + 7 n + 3 n + 1 n + 31 n + 15 n + 7 n + 3 n + 15 n + 7 n + 3 n + 1 1 dcm means decimation. table 11. ddc samples in each jesd204b link when chip decimation ratio = 2 real (i) output (complex to real enabled) complex (i/q) outputs (complex to real disabled) hb2 fir + hb1 fir (dcm 1 = 2) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 4) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb1 fir (dcm 1 = 2) hb2 fir + hb1 fir (dcm 1 = 4) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) n n n n n n n n + 1 n n n + 1 n n n n + 2 n + 1 n n + 2 n + 1 n n n + 3 n + 1 n n + 3 n + 1 n n n + 4 n + 2 n + 1 n + 4 n + 2 n + 1 n n + 5 n + 2 n + 1 n + 5 n + 2 n + 1 n n + 6 n + 3 n + 1 n + 6 n + 3 n + 1 n n + 7 n + 3 n + 1 n + 7 n + 3 n + 1 n n + 8 n + 4 n + 2 n + 8 n + 4 n + 2 n + 1 n + 9 n + 4 n + 2 n + 9 n + 4 n + 2 n + 1
ad6684 data sheet rev. 0 | page 36 of 107 real (i) output (complex to real enabled) complex (i/q) outputs (complex to real disabled) hb2 fir + hb1 fir (dcm 1 = 2) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 4) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb1 fir (dcm 1 = 2) hb2 fir + hb1 fir (dcm 1 = 4) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) n + 10 n + 5 n + 2 n + 10 n + 5 n + 2 n + 1 n + 11 n + 5 n + 2 n + 11 n + 5 n + 2 n + 1 n + 12 n + 6 n + 3 n + 12 n + 6 n + 3 n + 1 n + 13 n + 6 n + 3 n + 13 n + 6 n + 3 n + 1 n + 14 n + 7 n + 3 n + 14 n + 7 n + 3 n + 1 n + 15 n + 7 n + 3 n + 15 n + 7 n + 3 n + 1 1 dcm means decimation. table 12. ddc samples in each jesd204b link when chip decimation ratio = 4 real (i) output (complex to real enabled) complex (i/q) outputs (complex to real disabled) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 4) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb2 fir + hb1 fir (dcm 1 = 4) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) n n n n n n + 1 n n + 1 n n n + 2 n + 1 n + 2 n + 1 n n + 3 n + 1 n + 3 n + 1 n n + 4 n + 2 n + 4 n + 2 n + 1 n + 5 n + 2 n + 5 n + 2 n + 1 n + 6 n + 3 n + 6 n + 3 n + 1 n + 7 n + 3 n + 7 n + 3 n + 1 1 dcm means decimation. table 13. ddc samples in each jesd204b link when chip decimation ratio = 8 real (i) output (complex to real enabled) complex (i/q) outputs (complex to real disabled) hb4 fir + hb3 fir + hb 2 fir + hb1 fir (dcm 1 = 8) hb3 fir + hb2 fir + hb1 fir (dcm 1 = 8) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) n n n n + 1 n + 1 n n + 2 n + 2 n + 1 n + 3 n + 3 n + 1 n + 4 n + 4 n + 2 n + 5 n + 5 n + 2 n + 6 n + 6 n + 3 n + 7 n + 7 n + 3 1 dcm means decimation. table 14. ddc samples in each jesd204b li nk when chip decimation ratio = 16 real (i) output (complex to real enabled) complex (i/q) outputs (complex to real disabled) hb4 fir + hb3 fir + hb 2 fir + hb1 fir (dcm 1 = 16) hb4 fir + hb3 fir + hb2 fir + hb1 fir (dcm 1 = 16) not applicable n not applicable n + 1 not applicable n + 2 not applicable n + 3 1 dcm means decimation.
data sheet ad6684 rev. 0 | page 37 of 107 for example, if the chip decimation ratio is set to decimate by 4, ddc 0 is set to use hb2 + hb1 filters (complex outputs, decimate by 4) and ddc 1 is set to use hb4 + hb3 + hb2 + hb1 filters (real outputs, decimate by 8). ddc 1 repeats its output data two times for every one ddc 0 output. the resulting output samples are shown in table 15. table 15. ddc output samples in ea ch jesd204b link when chip dcm 1 = 4, ddc 0 dcm 1 = 4 (complex), and ddc 1 dcm 1 = 8 (real) ddc 0 ddc 1 ddc input samples output port i output port q output port i output port q n i0 (n) q0 (n) i1 (n) not applicable n + 1 n + 2 n + 3 n + 4 i0 (n + 1) q0 (n + 1) n + 5 n + 6 n + 7 n + 8 i0 (n + 2) q0 (n + 2) i1 (n + 1) not applicable n + 9 n + 10 n + 11 n + 12 i0 (n + 3) q0 (n + 3) n + 13 n + 14 n + 15 1 dcm means decimation.
ad6684 data sheet rev. 0 | page 38 of 107 frequency translation general description frequency translation is accomplished by using a 48-bit complex nco with a digital quadrature mixer. this stage translates either a real or complex input signal from an if to a baseband complex digital output (carrier frequency = 0 hz). the frequency translation stage of each ddc can be controlled individually and supports four different if modes using bits[5:4] of the ddc control registers (register 0x0310 and register 0x0330) in conjunction with the pair index register (register 0x0009). these if modes are ? variable if mode ? 0 hz if or zero if (zif) mode ? f s /4 hz if mode ? te s t mo d e variable if mode nco and mixers are enabled. nco output frequency can be used to digitally tune the if frequency. 0 hz if (zif) mode the mixers are bypassed, and the nco is disabled. f s /4 hz if mode the mixers and the nco are enabled in special downmixing by f s /4 mode to save power. test mode input samples are forced to 0.9599 to positive full scale. the nco is enabled. this test mode allows the ncos to directly drive the decimation filters. figure 75 and figure 76 show examples of the frequency translation stage for both real and complex inputs. bandwidth of interest bandwidth of interest image nco frequency tuning word (ftw) selection 48-bit nco ftw = mixing frequency/adc sample rate 2 48 adc + digital mixer + nco real input?sampled at f s cos( & t) 0 90 i q adc sampling at f s real real ?sin( & t) 48-bit nco positive ftw values negative ftw values complex ?6db loss due to nco + mixer 48-bit nco ftw = round (( f s /3)/ f s 2 48 ) = +9.3825 13 (0x555555555555) 48-bit nco ftw = round ((? f s /3)/ f s 2 48 ) = ?9.3825 13 (0xffff000000000000) 14994-057 dc ? f s /2 ? f s /4 ? f s /8 f s /16 f s /8 f s /4 f s /2 ? f s /16 ? f s /32 f s /32 ? f s /3 f s /3 dc ? f s /32 f s /32 dc ? f s /32 f s /32 figure 75. ddc nco frequency tuni ng word selection?real inputs
data sheet ad6684 rev. 0 | page 39 of 107 nco frequency tuning word (ftw) selection 48-bit nco ftw = mixing frequency/adc sample rate 2 48 quadrature analog mixer + 2 adcs + quadrature digital mixer + nco complex input?sampled at f s ? f s /32 f s /32 dc bandwidth of interest positive ftw values image due to analog i/q mismatch real i q quadrature mixer i q i ? + q q i q + + q i i complex i q ?sin( t) adc sampling at f s adc sampling at f s 90 phase 48-bit nco 90 0 48-bit nco ftw = round (( f s /3)/ f s 2 48 ) = +9.3825 13 (0x555555555555) 14994-058 ? f s /2 ? f s /3 ? f s /4 ? f s /8 f s /16 f s /8 f s /4 f s /3 f s /2 ? f s /16 ? f s /32 f s /32 dc figure 76. ddc nco frequency tuning word selectioncomplex inputs ddc nco + mixer loss and sfdr when mixing a real input signal down to baseband, 6 db of loss is introduced in the signal due to filtering of the negative image. an additional 0.05 db of loss is introduced by the nco. the total loss of a real input signal mixed down to baseband is 6.05 db. for this reason, it is recommended that the user compensate for this loss by enabling the 6 db of gain in the gain stage of the ddc to recenter the dynamic range of the signal within the full scale of the output bits. when mixing a complex input signal down to baseband, the maximum value that each i/q sample can reach is 1.414 full scale after it passes through the complex mixer. to avoid over- range of the i/q samples and to keep the data bit widths aligned with real mixing, 3.06 db of loss is introduced in the mixer for complex signals. an additional 0.05 db of loss is introduced by the nco. the total loss of a complex input signal mixed down to baseband is ?3.11 db. the worst case spurious signal from the nco is greater than 102 dbc sfdr for all output frequencies. numerically controlled oscillator the ad6684 has a 48-bit nco for each ddc that enables the frequency translation process. the nco allows the input spectrum to be tuned to dc, where it can be effectively filtered by the subsequent filter blocks to prevent aliasing. the nco can be set up by providing a frequency tuning word (ftw) and a phase offset word (pow). setting up the nco ftw and pow the nco frequency value is given by the 48-bit twos complement number entered in the nco ftw. frequencies between ?f s /2 and +f s /2 (f s /2 excluded) are represented using the following frequency words: x 0x8000 0000 0000 represents a frequency of ?f s /2. x 0x0000 0000 0000 represents dc (frequency is 0 hz). x 0x7fff ffff ffff represents a frequency of +f s /2 ? f s /2 48 . the nco frequency tuning word can be calculated using the following equation: s sc f ff ftwnco ,mod 2round _ 48 where: nco_ftw is a 48-bit twos complement number representing the nco ftw. f c is the desired carrier frequency in hz. f s is the ad6684 sampling frequency (clock rate) in hz. mod( ) is a remainder function. for example, mod(110,100) = 10 and for negative numbers, mod(C32,10) = ?2. round( ) is a rounding function. for example, round(3.6) = 4 and for negative numbers, round(C3.4) = ?3. note that this equation applies to the aliasing of signals in the digital domain (that is, aliasing introduced when digitizing analog signals).
ad6684 data sheet rev. 0 | page 40 of 107 for example, if the adc sampling frequency (f s ) is 500 msps and the carrier frequency (f c ) is 140.312 mhz, then nco_ftw = round ? ? ? ? ? ? ? ? ? ? 500 500,312.140mod 2 48 = 7.89886 10 13 hz this, in turn, converts to 0x47d in the 48-bit twos complement representation for nco_ftw. the actual carrier frequency, f c_actual , is calculated based on the following equation: f c_actual = 48 2 _ s fftw nco ? = 140.312 mhz a 48-bit pow is available for each nco to create a known phase relationship between multiple ad6684 chips or individual ddc channels inside one ad6684 chip. the pow registers can be updated in the nco at any time without disrupting the phase accumulators, allowing phase adjustments to occur during normal operation. however, the following procedure must be followed to update the ftw registers to ensure proper operation of the nco: 1. write to the ftw registers for all the ddcs. 2. synchronize the ncos either through the ddc nco soft reset bit (register 0x0300, bit 4), which is accessible through the spi, or through the assertion of the sysref pin. it is important to note that the ncos must be synchronized either through the spi or through the sysref pin after all writes to the ftw or pow registers are complete. this step is necessary to ensure the proper operation of the nco. nco synchronization each nco contains a separate phase accumulator word (paw). the initial reset value of each paw is set to zero, and the phase increment value of each paw is determined by the ftw. the pow is added to the paw to produce the instantaneous phase of the nco. see the setting up the nco ftw and pow section for more information. use the following two methods to synchronize multiple paws within the chip. ? using the spi. use the ddc nco soft reset bit in the ddc synchronization control register (register 0x0300, bit 4) to reset all the paws in the chip. this is accomplished by setting the ddc nco soft reset bit high and then setting this bit low. note that this method can only be used to synchronize ddc channels within the same pair (a/b or c/d) of a ad6684 chip. ? using the sysref pin. when the sysref pin is enabled in the sysref control registers (register 0x0120 and register 0x0121) and the ddc synchronization is enabled in the ddc synchronization control register (register 0x0300, bits[1:0]), any subsequent sysref event resets all the paws in the chip. note that this method can be used to synchronize ddc channels within the same ad6684 chip or ddc channels within separate ad6684 chips. mixer the nco is accompanied by a mixer. its operation is similar to an analog quadrature mixer. it performs the downconversion of input signals (real or complex) by using the nco frequency as a local oscillator. for real input signals, this mixer performs a real mixer operation (with two multipliers). for complex input signals, the mixer performs a complex mixer operation (with four multipliers and two adders). the mixer adjusts its operation based on the input signal (real or complex) provided to each individual channel. the selection of real or complex inputs can be controlled individually for each ddc block using bit 7 of the ddc control registers (register 0x0310 and register 0x0330) in conjunction with the pair index register (register 0x0009).
data sheet ad6684 rev. 0 | page 41 of 107 fir filters general description there are four sets of decimate by 2, low-pass, half-band, fir filters (labeled hb1 fir, hb2 fir, hb3 fir, and hb4 fir in figure 73) following the frequency translation stage. after the carrier of interest is tuned down to dc (carrier frequency = 0 hz), these filters efficiently lower the sample rate, while providing sufficient alias rejection from unwanted adjacent carriers around the bandwidth of interest. hb1 fir is always enabled and cannot be bypassed. the hb2, hb3, and hb4 fir filters are optional and can be bypassed for higher output sample rates. table 16 shows the different bandwidths selectable by including different half-band filters. in all cases, the ddc filtering stage on the ad6684 provides 100 db of stop-band alias rejection. table 17 shows the amount of stop-band alias rejection for multiple pass-band ripple/cutoff points. the decimation ratio of the filtering stage of each ddc can be controlled individually through bits[1:0] of the ddc control registers (register 0x0310 and register 0x0330) in conjunction with the pair index register (register 0x0009). table 16. ddc filter characteristics half band filter selection real output complex (i/q) output alias protected bandwidth (mhz) ideal snr improvement 1 (db) pass-band ripple (db) alias rejection (db) decimation ratio output sample rate (msps) decimation ratio output sample rate (msps) hb1 1 500 2 250 (i) + 250 (q) 200 1 100 hb1 + hb2 2 250 4 125 (i) + 125 (q) 100 4 hb1 + hb2 + hb3 4 125 8 62.5 (i) + 62.5 (q) 50 7 hb1 + hb2 + hb3 + hb4 8 62.5 16 31.25 (i) + 31.25 (q) 25 10 1 ideal snr improvement due to oversampling and filtering = 10log(bandwidth/(f s /2)). table 17. ddc filter alias rejection alias rejection (db) pass-band ripple/cutoff point (db) alias protected bandwidth for real (i) outputs 1 alias protected bandwidth for complex (i/q) outputs >100 ad6684 data sheet rev. 0 | page 42 of 107 half-band filters the ad6684 offers four half-band filters to enable digital signal processing of the adc converted data. these half-band filters are bypassable and can be individually selected. hb4 filter the first decimate by 2, half-band, low-pass, fir filter (hb4) uses an 11-tap, symmetrical, fixed coefficient filter implementa- tion that is optimized for low power consumption. the hb4 filter is only used when complex outputs (decimate by 16) or real outputs (decimate by 8) are enabled; otherwise, it is bypassed. table 18 and figure 77 show the coefficients and response of the hb4 filter. table 18. hb4 filter coefficients hb4 coefficient number decimal coefficient quantized coefficient (15-bit) c1, c11 0.006042 99 c2, c10 0 0 c3, c9 ?0.049377 ?809 c4, c8 0 0 c5, c7 0.293334 4806 c6 0.500000 8192 ?250 ?200 ?150 ?100 ?50 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 magnitude (db) 14994-059 normalized frequency ( rad/sample) figure 77. hb4 filter response hb3 filter the second decimate by 2, half-band, low-pass, fir filter (hb3) uses an 11-tap, symmetrical, fixed coefficient filter implementa- tion that is optimized for low power consumption. the hb3 filter is only used when complex outputs (decimate by 8 or 16) or real outputs (decimate by 4 or 8) are enabled; otherwise, it is bypassed. table 19 and figure 78 show the coefficients and response of the hb3 filter. table 19. hb3 filter coefficients hb3 coefficient number decimal coefficient quantized coefficient (17-bit) c1, c11 0.006638 435 c2, c10 0 0 c3, c9 ?0.051055 ?3,346 c4, c8 0 0 c5, c7 0.294418 19,295 c6 0.500000 32,768 ?180 ?100 ?60 ?40 ?20 ?160 ?140 ?120 ?80 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 magnitude (db) 14994-060 normalized frequency ( rad/sample) figure 78. hb3 filter response hb2 filter the third decimate by 2, half-band, low-pass, fir filter (hb2) uses a 19-tap, symmetrical, fixed coefficient filter implementa- tion that is optimized for low power consumption. the hb2 filter is only used when complex or real outputs (decimate by 4, 8, or 16) is enabled; otherwise, it is bypassed. table 20 and figure 79 show the coefficients and response of the hb2 filter. table 20. hb2 filter coefficients hb2 coefficient number decimal coefficient quantized coefficient (18-bit) c1, c19 0.000671 88 c2, c18 0 0 c3, c17 ?0.005325 ?698 c4, c16 0 0 c5, c15 0.022743 2,981 c6, c14 0 0 c7, c13 ?0.074181 ?9,723 c8, c12 0 0 c9, c11 0.306091 40,120 c10 0.500000 65,536
data sheet ad6684 rev. 0 | page 43 of 107 ?180 ?100 ?60 ?40 ?20 ?160 ?140 ?120 ?80 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 magnitude (db) 14994-061 normalized frequency ( rad/sample) figure 79. hb2 filter response hb1 filter the fourth and final decimate by 2, half-band, low-pass, fir filter (hb1) uses a 63-tap, symmetrical, fixed coefficient filter implementation that is optimized for low power consumption. the hb1 filter is always enabled and cannot be bypassed. table 21 and figure 80 show the coefficients and response of the hb1 filter. ?100 ?60 ?40 ?20 ?160 ?140 ?120 ?80 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 magnitude (db) 14994-062 normalized frequency ( rad/sample) figure 80. hb1 filter response table 21. hb1 filter coefficients hb1 coefficient number decimal coefficient quantized coefficient (20-bit) c1, c63 ?0.000019 ?10 c2, c62 0 0 c3, c61 0.000072 38 c4, c60 0 0 c5, c59 ?0.000194 ?102 c6, c58 0 0 c7, c57 0.000442 232 c8, c56 0 0 c9, c55 ?0.000891 ?467 c10, c54 0 0 c11, c53 0.001644 862 c12, c52 0 0 c13, c51 ?0.002840 ?1,489 c14, c50 0 0 c15, c49 0.004653 2,440 c16, c48 0 0 c17, c47 ?0.007311 ?3,833 c18, c46 0 0 c19, c45 0.011121 5,831 c20, c44 0 0 c21, c43 ?0.016553 ?8,679 c22, c42 0 0 c23, c41 0.024420 12,803 c24, c40 0 0 c25, c39 ?0.036404 ?19,086 c26, c38 0 0 c27, c37 0.056866 29,814 c28, c36 0 0 c29, c35 ?0.101892 ?53,421 c30, c34 0 0 c31, c33 0.316883 166,138 c32 0.500000 262,144
ad6684 data sheet rev. 0 | page 44 of 107 ddc gain stage each ddc contains an independently controlled gain stage. the gain is selectable as either 0 db or 6 db. when mixing a real input signal down to baseband, it is recommended that the user enable the 6 db of gain to recenter the dynamic range of the signal within the full scale of the output bits. when mixing a complex input signal down to baseband, the mixer has already recentered the dynamic range of the signal within the full scale of the output bits, and no additional gain is necessary. however, the optional 6 db gain compensates for low signal strengths. the downsample by 2 portion of the hb1 fir filter is bypassed when using the complex to real conversion stage. ddc complex to real conversion each ddc contains an independently controlled complex to real conversion block. the complex to real conversion block reuses the last filter (hb1 fir) in the filtering stage along with an f s /4 complex mixer to upconvert the signal. after upconvert- ing the signal, the q portion of the complex mixer is no longer needed and is dropped. figure 81 shows a simplified block diagram of the complex to real conversion. low-pass filter 2 i q real hb1 fir low-pass filter 2 hb1 fir 0 1 complex to real enable q 90 0 + ? complex to real conversion i q i q gain stage cos( t) sin( t) f s /4 i/real 0db or 6db 0db or 6db 0db or 6db 0db or 6db 14994-063 figure 81. complex to real conversion block
data sheet ad6684 rev. 0 | page 45 of 107 ddc example configurations table 22 describes the register settings for multiple ddc example configurations. table 22. ddc example configurations (per adc channel pair) chip application layer chip decimation ratio ddc input type ddc output type bandwidth per ddc 1 no. of virtual converters required register settings 2 one ddc 2 complex complex 40% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x01 (one ddc; i/q selected) 0x0201 = 0x01 (chip decimate by 2) 0x0310 = 0x83 (complex mixer; 0 db gain; variable if; complex outputs; hb1 filter) 0x0311 = 0x04 (ddc i input = adc channel a/ channel c; ddc q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 one ddc 4 complex complex 20% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x01 (one ddc; i/q selected) 0x0201 = 0x02 (chip decimate by 4) 0x0310= 0x80 (complex mixer; 0 db gain; variable if; complex outputs; hb2 + hb1 filters) 0x0311= 0x04 (ddc i input = adc channel a/ channel c; ddc q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 two ddcs 2 real real 20% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x22 (two ddcs; i only selected) 0x0201 = 0x01 (chip decimate by 2) 0x0310, 0x0330 = 0x48 (real mixer; 6 db gain; variable if; real output; hb2 + hb1 filters) 0x0311 = 0x00 (ddc 0 i input = adc channel a/ channel c; ddc 0 q input = adc channel a/ channel c) 0x0331 = 0x05 (ddc 1 i input = adc channel b/ channel d; ddc 1 q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342 = ftw and pow set as required by application for ddc 1
ad6684 data sheet rev. 0 | page 46 of 107 chip application layer chip decimation ratio ddc input type ddc output type bandwidth per ddc 1 no. of virtual converters required register settings 2 two ddcs 2 complex complex 40% f s 4 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x22 (two ddcs; i only selected) 0x0201 = 0x01 (chip decimate by 2) 0x0310, 0x0330 = 0x4b (complex mixer; 6 db gain; variable if; complex output; hb1 filter) 0x0311, 0x0331 = 0x04 (ddc 0 i input = adc channel a/channel c; ddc 0 q input = adc channel b/channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1 two ddcs 4 complex complex 20% f s 4 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x02 (two ddcs; i/q selected) 0x0201 = 0x02 (chip decimate by 4) 0x0310, 0x0330 = 0x80 (complex mixer; 0 db gain; variable if; complex outputs; hb2 + hb1 filters) 0x0311, 0x0331 = 0x04 (ddc i input = adc channel a/channel c; ddc q input = adc channel b/channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1 two ddcs 4 complex real 10% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x22 (two ddcs; i only selected) 0x0201 = 0x02 (chip decimate by 4) 0x0310, 0x0330 = 0x89 (complex mixer; 0 db gain; variable if; real output; hb3 + hb2 + hb1 filters) 0x0311, 0x0331 = 0x04 (ddc i input = adc channel a/channel c; ddc q input = adc channel b/channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1
data sheet ad6684 rev. 0 | page 47 of 107 chip application layer chip decimation ratio ddc input type ddc output type bandwidth per ddc 1 no. of virtual converters required register settings 2 two ddcs 4 real real 10% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x22 (two ddcs; i only selected) 0x0201 = 0x02 (chip decimate by 4) 0x0310, 0x0330 = 0x49 (real mixer; 6 db gain; variable if; real output; hb3 + hb2 + hb1 filters) 0x0311 = 0x00 (ddc 0 i input = adc channel a/ channel c; ddc 0 q input = adc channel a/ channel c) 0x0331 = 0x05 (ddc 1 i input = adc channel b/ channel d; ddc 1 q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1 two ddcs 4 real complex 20% f s 4 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x02 (two ddcs; i/q selected) 0x0201 = 0x02 (chip decimate by 4) 0x0310, 0x0330 = 0x40 (real mixer; 6 db gain; variable if; complex output; hb2 + hb1 filters) 0x0311 = 0x00 (ddc 0 i input = adc channel a/ channel c; ddc 0 q input = adc channel a/ channel c) 0x0331 = 0x05 (ddc 1 i input = adc channel b/ channel d; ddc 1 q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1
ad6684 data sheet rev. 0 | page 48 of 107 chip application layer chip decimation ratio ddc input type ddc output type bandwidth per ddc 1 no. of virtual converters required register settings 2 two ddcs 8 real real 5% f s 2 0x0009 = 0x01, 0x02, or 0x03 (pair selection) 0x0200 = 0x22 (two ddcs; i only selected) 0x0201 = 0x03 (chip decimate by 8) 0x0310, 0x0330 = 0x4a (real mixer; 6 db gain; variable if; real output; hb4 + hb3 + hb2 + hb1 filters) 0x0311 = 0x00 (ddc 0 i input = adc channel a/ channel c; ddc 0 q input = adc channel a/ channel c) 0x0331 = 0x05 (ddc 1 i input = adc channel b/ channel d; ddc 1 q input = adc channel b/ channel d) 0x0314, 0x0315, 0x0316, 0x0317, 0x0318, 0x031a, 0x031d, 0x031e, 0x031f, 0x0320, 0x0321, 0x0322 = ftw and pow set as required by application for ddc 0 0x0334, 0x0335, 0x0336, 0x0337, 0x0338, 0x033a, 0x033d, 0x033e, 0x033f, 0x0340, 0x0341, 0x0342= ftw and pow set as required by application for ddc 1 1 f s is the adc sample rate. band widths listed are 100 db of stop-band alias rejection. 2 the ncos must be synchronized either through the spi or through the sysref pin after all writes to the ftw or pow registers h ave completed. this is necessary to ensure the proper operation of the nco. see the nco synchronization sectio n for more information.
data sheet ad6684 rev. 0 | page 49 of 107 noise shaping requantizer (nsr) when operating the ad6684 with the nsr enabled, a decimating half-band filter that is optimized at certain input frequency bands can also be enabled. this filter offers the user the flexibility in signal bandwidth processing and image rejection. careful frequency planning can offer advantages in analog filtering preceding the adc. the filter can function either in high-pass or low-pass mode. the filter can be optionally enabled on the ad6684 when the nsr is enabled. when operating with the nsr enabled, the decimating half-band filter mode (low pass or high pass) is selected by setting bit 7 in register 0x041e. when the decimating half-band filter is enabled, the chip decimation ratio register (register 0x0201) must be set to a decimation rate of 2 (register value = 0x01). decimating half-band filter the ad6684 optional decimating half-band filter reduces the input sample rate by a factor of 2 while rejecting aliases that fall into the band of interest. for an input sample clock of 500 mhz, this filter reduces the output sample rate to 250 msps. this filter is designed to provide >40 db of alias protection for 39.5% of the output sample rate (79% of the nyquist band). for an adc sample rate of 500 msps, the filter provides a maximum usable bandwidth of 98.75 mhz. half-band filter coefficients the 19-tap, symmetrical, fixed coefficient half-band filter has low power consumption due to its polyphase implementation. table 23 lists the coefficients of the half-band filter in low-pass mode. in high-pass mode, coefficient c9 is multiplied by ?1. the decimal coefficients used in the implementation and the decimal equivalent values of the coefficients are listed. coefficients not listed in table 23 are 0s. table 23. fixed coefficients for half-band filter coefficient number decimal coefficient quantized coefficient (12-bit) 0 0.012207 25 c2, c16 ?0.022949 ?47 c4, c14 0.045410 93 c6, c12 ?0.094726 ?194 c8, c10 0.314453 644 c9 0.500000 1024 half-band filter features the half-band decimating filter provides approximately 39.5% of the output sample rate in usable bandwidth (19.75% of the input sample clock). the filter provides >40 db of rejection. the normalized response of the half-band filter in low-pass mode is shown in figure 82. in low-pass mode, operation is allowed in the first nyquist zone, which includes frequencies of up to f s /2, where f s is the decimated sample rate. for example, with an input clock of 500 mhz, the output sample rate is 250 msps and f s /2 = 125 mhz. ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 10 0 0.05 0.10 0.15 0.20 0.25 normalized frequency ( rad/sample) magnitude (db) 0.30 0.35 0.40 0.45 0.50 14994-064 figure 82. low-pass, half-band filter response the half-band filter can also be used in high-pass mode. the usable bandwidth remains at 39.5% of the output sample rate (19.75% of the input sample clock), which is the same as in low- pass mode). figure 83 shows the normalized response of the half-band filter in high-pass mode. in high-pass mode, operation is allowed in the second and third nyquist zones, which includes frequencies from f s /2 to 3f s /2, where f s is the decimated sample rate. for example, with an input clock of 500 mhz, the output sample rate is 250 msps, f s /2 = 125 mhz, and 3f s /2 = 375 mhz. ?80 ?70 ?60 ?50 ?40 ?30 ?20 ?10 0 10 0 0.1 0.2 0.3 0.4 0.5 normalized frequency ( rad/sample) magnitude (db) 0.6 0.7 0.8 0.9 1.0 14994-065 figure 83. high-pass, half-band filter response
ad6684 data sheet rev. 0 | page 50 of 107 nsr overview the ad6684 features an nsr to allow higher than 9-bit snr to be maintained in a subset of the nyquist band. the harmonic performance of the receiver is unaffected by the nsr feature. when enabled, the nsr contributes an additional 3.0 db of loss to the input signal, such that a 0 dbfs input is reduced to ?3.0 dbfs at the output pins. this loss does not degrade the snr performance of the ad6684. the nsr feature can be independently controlled per channel via the spi. two different bandwidth modes are provided; select the mode from the spi port. in each of the two modes, the center frequency of the band can be tuned such that ifs can be placed anywhere in the nyquist band. the nsr feature is enabled by default on the ad6684 . the bandwidth and mode of the nsr operation are selected by setting the appropriate bits in register 0x0420 and register 0x0422. by selecting the appropriate profile and mode bits in these two registers, the nsr feature can be enabled for the desired mode of operation. 21% bw mode (>100 mhz at 491.52 msps) the first nsr mode offers excellent noise performance across a bandwidth that is 21% of the adc output sample rate (42% of the nyquist band) and can be centered by setting the nsr mode bits in the nsr mode register (address 0x0420) to 000. in this mode, the useful frequency range can be set using the 6-bit tuning word in the nsr tuning register (address 0x0422). there are 59 possible tuning words (tw), from 0 to 58; each step is 0.5% of the adc sample rate. the following three equations describe the left band edge (f 0 ), the channel center (f center ), and the right band edge (f 1 ), respectively: f 0 = f adc 0.005 tw f center = f 0 + 0.105 f adc f 1 = f 0 + 0.21 f adc 28% bw mode (>130 mhz at 491.52 msps) the second nsr mode offers excellent noise performance across a bandwidth that is 28% of the adc output sample rate (56% of the nyquist band) and can be centered by setting the nsr mode bits in the nsr mode register (address 0x0420) to 001. in this mode, the useful frequency range can be set using the 6-bit tuning word in the nsr tuning register (address 0x0422). there are 44 possible tuning words (tw, from 0 to 43); each step is 0.5% of the adc sample rate. the following three equations describe the left band edge (f 0 ), the channel center (f center ), and the right band edge (f 1 ), respectively: f 0 = f adc 0.005 tw f center = f 0 + 0.14 f adc f 1 = f 0 + 0.28 f adc
data sheet ad6684 rev. 0 | page 51 of 107 variable dynamic range (vdr) the ad6684 features a vdr digital processing block to allow up to a 14-bit dynamic range to be maintained in a subset of the nyquist band. across the full nyquist band, a minimum 9-bit dynamic range is available at all times. this operation is suitable for applications such as dpd processing. the harmonic perfor- mance of the receiver is unaffected by this feature. when enabled, vdr does not contribute loss to the input signal but operates by effectively changing the output resolution at the output pins. this feature can be independently controlled per channel via the spi. the vdr block operates in either complex or real mode. in complex mode, vdr has selectable bandwidths of 25% and 43% of the output sample rate. in real mode, the bandwidth of operation is limited to 25% of the output sample rate. the bandwidth and mode of the vdr operation are selected by setting the appropriate bits in register 0x0430. when the vdr block is enabled, input signals that violate a defined mask (signified by the gray shaded areas in figure 84) result in the reduction of the output resolution of the ad6684. the vdr block analyzes the peak value of the aggregate signal level in the disallowed zones to determine the reduction of the output resolution. to indicate that the ad6684 is reducing output, the resolution vdr punish bits and/or a vdr high/low resolution bit can optionally be inserted into the output data stream as control bits by programming the appropriate value into register 0x0559 and register 0x055a. up to two control bits can be used without the need to change the converter resolution parameter, n. up to three control bits can be used, but if using three, the converter resolution parameter, n, must be changed to 13. the vdr high/low resolution bit can be programmed into either of the three available control bits and indicates if vdr is reducing output resolution (bit value is a 1), or if full resolution is available (bit value is a 0). enable the two punish bits to provide a clearer indication of the available resolution of the sample. to decode these two bits, see table 24. table 24. vdr reduced outp ut resolution values vdr punish bits[1:0] output resolution (bits) 00 14 01 13 10 12 or 11 11 10 or 9 the frequency zones of the mask are defined by the bandwidth mode selected in register 0x0430. the upper amplitude limit for input signals located in these frequency zones is ?30 dbfs. if the input signal level in the disallowed frequency zones exceeds an amplitude level of C30 dbfs (into the gray shaded areas), the vdr block triggers a reduction in the output resolution, as shown in figure 84. the vdr block engages and begins limiting output resolution gradually as the signal amplitudes increase in the mask regions. as the signal amplitude level increases into the mask regions, the output resolution is gradually lowered. for every 6 db increase in signal level above ?30 dbfs, one bit of output resolution is discarded from the output data by the vdr block, as shown in table 25. these zones can be tuned within the nyquist band by setting bits[3:0] in register 0x0434 to determine the vdr center frequency (f vdr ). the vdr center frequency in complex mode ca n be adjusted from 1/16 f s to 15/16 f s in 1/16 f s steps. in real mode, f vdr can be adjusted from 1/8 f s to 3/8 f s in 1/16 f s steps. table 25. vdr reduced outp ut resolution values signal amplitude violating defined vdr mask output resolution (bits) amplitude ?30 dbfs 14 ?30 dbfs < amplitude ?24 dbfs 13 ?24 dbfs < amplitude ?18 dbfs 12 ?18 dbfs < amplitude ?12 dbfs 11 ?12 dbfs < amplitude ?6 dbfs 10 ?6 dbfs < amplitude 0 dbfs 9 dbfs ?30 0 intermodulation products < ?30dbfs intermodulation products > ?30dbfs f s 0 f s 14994-072 figure 84. vdr operation?reduct ion in output resolution
ad6684 data sheet rev. 0 | page 52 of 107 vdr real mode the real mode of vdr works over a bandwidth of 25% of the sample rate (50% of the nyquist band). the output bandwidth of the ad6684 can be 25% only when operating in real mode. figure 85 shows the frequency zones for the 25% bandwidth real output vdr mode tuned to a center frequency (f vdr ) of f s /4 (tuning word = 0x04). the frequency zones where the amplitude cannot exceed ?30 dbfs are the upper and lower portions of the nyquist band signified by the gray shaded areas. dbfs ?30 01/8 f s 3/8 f s 1/2 f s 14994-073 figure 85. 25% vdr bandwidth, real mode the center frequency (f vdr ) of the vdr function can be tuned within the nyquist band from 1/8 f s to 3/8 f s in 1/16 f s steps. in real mode, tuning word 2 (0x02) through tuning word 6 (0x06) are valid. table 26 shows the relative frequency values, and table 27 shows the absolute frequency values based on a sample rate of 491.52 msps. table 26. vdr tuning words and relative frequency values, 25% bw, real mode tuning word lower band edge center frequency upper band edge 2 (0x02) 0 1/8 f s 1/4 f s 3 (0x03) 1/16 f s 3/16 f s 5/16 f s 4 (0x04) 1/8 f s 1/4 f s 3/8 f s 5 (0x05) 3/16 f s 5/16 f s 7/16 f s 6 (0x06) 1/4 f s 3/8 f s 1/2 f s table 27. vdr tuning words and absolute frequency values, 25% bw, real mode (f s = 491.52 msps) tuning word lower band edge (mhz) center frequency (mhz) upper band edge (mhz) 2 (0x02) 0 61.44 122.88 3 (0x03) 30.72 92.16 153.6 4 (0x04) 61.44 122.88 184.32 5 (0x05) 92.16 153.6 215.04 6 (0x06) 122.88 184.32 245.76 vdr complex mode the complex mode of vdr works with selectable bandwidths of 25% of the sample rate (50% of the nyquist band) and 43% of the sample rate (86% of the nyquist band). figure 86 and figure 87 show the frequency zones for vdr in the complex mode. when operating vdr in complex mode, place in-phase (i) input signal data in channel a and place quadrature (q) signal data in channel b. figure 86 shows the frequency zones for the 25% bandwidth vdr mode with a center frequency of f s /4 (tuning word = 0x04). the frequency zones where the amplitude may not exceed ?30 dbfs are the upper and lower portions of the nyquist band extending into the complex domain. ?30 dbfs 1/8 f s 3/8 f s 1/2 f s ?1/2 f s 0 14994-074 figure 86. 25% vdr bandwidth, complex mode the center frequency (f vdr ) of the vdr function can be tuned within the nyquist band from 0 to 15/16 f s in 1/16 f s steps. in complex mode, tuning word 0 (0x00) through tuning word 15 (0x0f) are valid. table 28 and table 29 show the tuning words and frequency values for the 25% complex mode. table 28 shows the relative frequency values, and table 29 shows the absolute frequency values based on a sample rate of 491.52 msps. table 28. vdr tuning words and relative frequency values, 25% bw, complex mode tuning word lower band edge center frequency upper band edge 0 (0x00) ?1/8 f s 0 1/8 f s 1 (0x01) ?1/16 f s 1/16 f s 3/16 f s 2 (0x02) 0 1/8 f s 1/4 f s 3 (0x03) 1/16 f s 3/16 f s 5/16 f s 4 (0x04) 1/8 f s 1/4 f s 3/8 f s 5 (0x05) 3/16 f s 5/16 f s 7/16 f s 6 (0x06) 1/4 f s 3/8 f s 1/2 f s 7 (0x07) 5/16 f s 7/16 f s 9/16 f s 8 (0x08) 3/8 f s 1/2 f s 5/8 f s 9 (0x09) 7/16 f s 9/16 f s 11/16 f s 10 (0x0a) 1/2 f s 5/8 f s 3/4 f s 11 (0x0b) 9/16 f s 11/16 f s 13/16 f s 12 (0x0c) 5/8 f s 3/4 f s 7/8 f s 13 (0x0d) 11/16 f s 13/16 f s 15/16 f s 14 (0x0e) 3/4 f s 7/8 f s f s 15 (0x0f) 13/16 f s 15/16 f s 17/16 f s
data sheet ad6684 rev. 0 | page 53 of 107 table 29. vdr tuning words and absolute frequency values, 25% bw, complex mode (f s = 491.52 msps) tuning word lower band edge (mhz) center frequency (mhz) upper band edge (mhz) 0 (0x00) ?61.44 0.00 61.44 1 (0x01) ?30.72 30.72 92.16 2 (0x02) 0.00 61.44 122.88 3 (0x03) 30.72 92.16 153.6 4 (0x04) 61.44 122.88 184.32 5 (0x05) 92.16 153.6 215.04 6 (0x06) 122.88 184.32 245.76 7 (0x07) 153.6 215.04 276.48 8 (0x08) 184.32 245.76 307.2 9 (0x09) 215.04 276.48 337.92 10 (0x0a) 245.76 307.2 368.64 11 (0x0b) 276.48 337.92 399.36 12 (0x0c) 307.2 368.64 430.08 13 (0x0d) 337.92 399.36 460.8 14 (0x0e) 368.64 430.08 491.52 15 (0x0f) 399.36 460.8 522.24 table 30 and table 31 show the tuning words and frequency values for the 43% complex mode. table 30 shows the relative frequency values, and table 31 shows the absolute frequency values based on a sample rate of 491.52 msps. figure 87 shows the frequency zones for the 43% bw vdr mode with a center frequency (f vdr ) of f s /4 (tuning word = 0x04). the frequency zones where the amplitude may not exceed ?30 dbfs are the upper and lower portions of the nyquist band extending into the complex domain. dbfs 1/29 f s 1/4 f s 20/43 f s 1/2 f s ?1/2 f s 0 ? 30 14994-075 figure 87. 43% vdr bandwidth, complex mode table 30. vdr tuning words and relative frequency values, 43% bw, complex mode tuning word lower band edge (mhz) center frequency (mhz) upper band edge (mhz) 0 (0x00) ?14/65 f s 0 14/65 f s 1 (0x01) ?11/72 f s 1/16 f s 5/18 f s 2 (0x02) ?1/11 f s 1/8 f s 16/47 f s 3 (0x03) ?1/36 f s 3/16 f s 29/72 f s 4 (0x04) 1/29 f s 1/4 f s 20/43 f s 5 (0x05) 7/72 f s 5/16 f s 19/36 f s 6 (0x06) 4/25 f s 3/8 f s 49/83 f s 7 (0x07) 2/9 f s 7/16 f s 47/72 f s 8 (0x08) 2/7 f s 1/2 f s 5/7 f s 9 (0x09) 25/72 f s 9/16 f s 7/9 f s 10 (0x0a) 34/83 f s 5/8 f s 21/25 f s 11 (0x0b) 17/36 f s 11/16 f s 65/72 f s 12 (0x0c) 23/43 f s 3/4 f s 28/29 f s 13 (0x0d) 43/72 f s 13/16 f s 37/36 f s 14 (0x0e) 31/47 f s 7/8 f s 12/11 f s 15 (0x0f) 13/18 f s 15/16 f s 83/72 f s table 31. vdr tuning words and absolute frequency values, 43% bw, complex mode (f s = 491.52 msps) tuning word lower band edge (mhz) center frequency (mhz) upper band edge (mhz) 0 (0x00) ?105.37 0.00 105.87 1 (0x01) ?75.09 30.72 136.53 2 (0x02) ?44.68 61.44 167.33 3 (0x03) ?13.65 92.16 197.97 4 (0x04) 16.95 122.88 228.61 5 (0x05) 47.79 153.6 259.41 6 (0x06) 78.64 184.32 290.17 7 (0x07) 109.23 215.04 320.85 8 (0x08) 140.43 245.76 351.09 9 (0x09) 170.67 276.48 382.29 10 (0x0a) 201.35 307.2 412.88 11 (0x0b) 232.11 337.92 443.73 12 (0x0c) 262.91 368.64 474.57 13 (0x0d) 293.55 399.36 505.17 14 (0x0e) 324.19 430.08 536.2 15 (0x0f) 354.99 460.8 566.61
ad6684 data sheet rev. 0 | page 54 of 107 digital outputs introduction to th e jesd204b interface the ad6684 digital outputs are designed to the jedec standard jesd204b, serial interface for data converters. jesd204b is a protocol to link the ad6684 to a digital processing device over a serial interface with lane rates of up to 15 gbps. the benefits of the jesd204b interface over lvds include a reduction in required board area for data interface routing, and an ability to enable smaller packages for converter and logic devices. jesd204b overview the jesd204b data transmit blocks assemble the parallel data from the adc into frames and uses 8-bit/10-bit encoding as well as optional scrambling to form serial output data. lane synchronization is supported through the use of special control characters during the initial establishment of the link. additional control characters are embedded in the data stream to maintain synchronization thereafter. a jesd204b receiver is required to complete the serial link. for additional details on the jesd204b interface, refer to the jesd204b standard. the jesd204b data transmit blocks in the ad6684 map up to two physical adcs or up to four virtual converters (when the ddcs are enabled) over each of the two jesd204b links. each link can be configured to use one or two jesd204b lanes for up to a total of four lanes for the ad6684 chip. the jesd204b specification refers to a number of parameters to define the link, and these parameters must match between the jesd204b transmitter (the ad6684 output) and the jesd204b receiver (the logic device input). the jesd204b outputs of the ad6684 function effectively as two individual jesd204b links. the two jesd204b links can be synchronized, if desired, using the sysref input. each jesd204b link is described according to the following parameters: ? l = number of lanes per converter device (lanes per link) ( ad6684 value = 1 or 2) ? m = number of converters per converter device (virtual converters per link) ( ad6684 value = 1, 2, or 4) ? f = octets per frame ( ad6684 value = 1, 2, 4, or 8) ? n? = number of bits per sample (jesd204b word size) ( ad6684 value = 8 or 16) ? n = converter resolution ( ad6684 value = 7 to 16) ? cs = number of control bits per sample ( ad6684 value = 0, 1, 2, or 3) ? k = number of frames per multiframe ( ad6684 value = 4, 8, 12, 16, 20, 24, 28, or 32 ) ? s = samples transmitted per single converter per frame cycle ( ad6684 value = set automatically based on l, m, f, and n?) ? hd = high density mode ( ad6684 = set automatically based on l, m, f, and n?) ? cf = number of control words per frame clock cycle per converter device ( ad6684 value = 0) figure 88 shows a simplified block diagram of the ad6684 jesd204b link. by default, the ad6684 is configured to use four converters and four lanes. the converter a and converter b data is output to serdoutab0 and serdoutab1, and the converter c and converter d data is output to serdoutcd0 and serdoutcd1. the ad6684 allows other configurations, such as combining the outputs of each pair of converters into a single lane, or changing the mapping of the digital output paths. these modes are set up via a quick configuration register in the spi register map, along with additional customizable options. by default in the ad6684 , the 14-bit converter word from each converter is broken into two octets (eight bits of data). bit 13 (ms b) through bit 6 are in the first octet. the second octet contains bit 5 through bit 0 (lsb) and two tail bits. the tail bits can be configured as zeros or a pseudorandom number sequence. the tail bits can also be replaced with control bits indicating overrange, sysref, vdr punish bits, or fast detect output. control bits are filled and inserted msb first such that enabling cs = 1 activates control bit 2, enabling cs = 2 activates control bit 2 and control bit 1, and enabling cs = 3 activates control bit 2, control bit 1, and control bit 0. the two resulting octets can be scrambled. scrambling is optional; however, it is recommended to avoid spectral peaks when transmitting similar digital data patterns. the scrambler uses a self synchronizing, polynomial-based algorithm defined by the equation 1 + x 14 + x 15 . the descrambler in the receiver is a self synchronizing version of the scrambler polynomial. the two octets are then encoded with an 8-bit/10-bit encoder. the 8-bit/10-bit encoder works by taking eight bits of data (an octet) and encoding them into a 10-bit symbol. figure 89 shows how the 14-bit data is taken from the adc, the tail bits are added, the two octets are scrambled, and how the octets are encoded into two 10-bit symbols. figure 89 shows the default data format.
data sheet ad6684 rev. 0 | page 55 of 107 mux/ format (spi registers: 0x0561, 0x0564) mux/ format (spi registers: 0x0561, 0x0564) jesd204b pair a/b link control (l, m, f) (spi register 0x0570) jesd204b pair a/b link control (l, m, f) (spi register 0x0570) lane mux and mapping (spi registers: 0x05b0, 0x05b2, 0x05b3) lane mux and mapping (spi registers: 0x05b0, 0x05b2, 0x05b3) converter a input converter b input converter c input converter d input adc a adc b adc c adc d serdoutab0+ serdoutab0? serdoutab1+ serdoutab1? serdoutcd0+ serdoutcd0? serdoutcd1+ serdoutcd1? sysref syncinab syncincd 14994-076 fig ure 88. transmit link simplified block diagram showing full bandwidth mode (register 0x0200 = 0x00) jesd204b sample construction serdoutab0/ serdoutcd0/ serdoutab0/ serdoutcd0/ tail bits reg 0x0571[6] frame construction scrambler 1 + x 14 + x 15 (optional) 8-bit/10-bit encoder serializer adc adc test patterns (reg 0x0550, reg 0x0551 to reg 0x0558) jesd204b long transport test pattern reg 0x0571[5] jesd204b data link layer test patterns reg 0x0574[2:0] msb lsb symbol0 symbol1 a a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1 a0 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1 a0 c2 t octet0 octet1 octet0 octet1 msb lsb s7 s6 s5 s4 s3 s2 s1 s0 msb lsb b c d e f g h i j a b . . . . . . . . a b i j i j a b c d e f g h i j c2 c1 c0 control bits jesd204b interface test patterns (reg 0x0573, reg 0x0551 to reg 0x0558) s7 s6 s5 s4 s3 s2 s1 s0 14994-077 figure 89. ad c output datapath showing data framing transport layer physical layer data link layer tx output sample construction frame construction scrambler alignment character generation 8-bit/10-bit encoder crossbar mux serializer processed samples from adc sysref syncinb 14994-078 figure 90. d ata flow
ad6684 data sheet rev. 0 | page 56 of 107 functional overview the block diagram in figure 90 shows the flow of data through each of the two jesd204b links from the sample input to the physical output. the processing can be divided into layers that are derived from the open source initiative (osi) model widely used to describe the abstraction layers of communications systems. these layers are the transport layer, data link layer, and physical layer (serializer and output driver). transport layer the transport layer handles packing the data (consisting of samples and optional control bits) into jesd204b frames that are mapped to 8-bit octets. these octets are sent to the data link layer. the transport layer mapping is controlled by rules derived from the link parameters. tail bits are added to fill gaps where required. the following equation can be used to determine the number of tail bits within a sample (jesd204b word): t = nfi C n C cs data link layer the data link layer is responsible for the low level functions of passing data across the link. these functions include optionally scrambling the data, inserting control characters for multichip synchronization, lane alignment, or monitoring, and encoding 8-bit octets into 10-bit symbols. the data link layer is also responsible for sending the initial lane alignment sequence (ilas), which contains the link configuration data used by the receiver to verify the settings in the transport layer. physical layer the physical layer consists of the high speed circuitry clocked at the serial clock rate. in this layer, parallel data is converted into one, two, or four lanes of high speed differential serial data. jesd204b link establishment the ad6684 jesd204b transmitter (tx) interface operates in subclass 1 as defined in the jedec standard 204b (july 2011 specification). the link establishment process is divided into the following steps: code group synchronization and syncinbab/ syncinbcd, initial lane alignment sequence, and user data and error correction. code group synchronization (cgs) and syncinb the cgs is the process by which the jesd204b receiver finds the boundaries between the 10-bit symbols in the stream of data. during the cgs phase, the jesd204b transmit block transmits /k28.5/ characters. the receiver must locate /k28.5/ characters in its input data stream using clock and data recovery (cdr) techniques. the receiver issues a synchronization request by asserting the syncinbab and syncinbcd pins of the ad6684 low. the jesd204b tx then begins sending /k/ characters. after the receiver synchronizes, it waits for the correct reception of at least four consecutive /k/ symbols. it then deasserts syncinbab and syncinbcd. the ad6684 then transmits an ilas on the following local multiframe clock (lmfc) boundary. for more information on the code group synchronization phase, refer to the jedec standard jesd204b, july 2011, section 5.3.3.1. the syncinbab and syncinbcd pin operation can also be controlled by the spi. the syncinbab and syncinbcd signals are differential lvds mode signals by default, but can also be driven single-ended. for more information on configuring the syncinbab and syncinbcd pin operation, refer to register 0x0572. initial lane alignment sequence (ilas) the ilas phase follows the cgs phase and begins on the next lmfc boundary. the ilas consists of four mulitframes, with an /r/ character marking the beginning and an /a/ character marking the end. the ilas begins by sending an /r/ character followed by 0 to 255 ramp data for one multiframe. on the second multiframe, the link configuration data is sent, starting with the third character. the second character is a /q/ character to confirm that the link configuration data follows. all undefined data slots are filled with ramp data. the ilas sequence is never scrambled. the ilas sequence construction is shown in figure 91. the four multiframes include the following: ? multiframe 1. begins with an /r/ character (/k28.0/) and ends with an /a/ character (/k28.3/). ? multiframe 2. begins with an /r/ character followed by a /q/ (/k28.4/) character, followed by link configuration parameters over 14 configuration octets (see table 32) and ends with an /a/ character. many of the parameter values are of the value C 1 notation. ? multiframe 3. begins with an /r/ character (/k28.0/) and ends with an /a/ character (/k28.3/). ? multiframe 4. begins with an /r/ character (/k28.0/) and ends with an /a/ character (/k28.3/). k k r d d a r q c c d d a r d d a r d d a d start of ilas start of link configuration data end of multiframe start of user data 14994-079 figure 91. initial lane alignment sequence
data sheet ad6684 rev. 0 | page 57 of 107 user data and error detection after the initial lane alignment sequence is complete, the user data is sent. normally, within a frame, all characters are considered user data. however, to monitor the frame clock and multiframe clock synchronization, there is a mechanism for replacing characters with /f/ or /a/ alignment characters when the data meets certain conditions. these conditions are different for unscrambled and scrambled data. the scrambling operation is enabled by default, but it can be disabled using the spi. for scrambled data, any 0xfc character at the end of a frame is replaced with an /f/, and any 0xfd character at the end of a multi- frame is replaced with an /a/. the jesd204b receiver (rx) checks for /f/ and /a/ characters in the received data stream and verifies that they only occur in the expected locations. if an unexpected /f/ or /a/ character is found, the receiver handles the situation by using dynamic realignment or asserting the syncinb signal for more than four frames to initiate a resynchronization. for unscrambled data, if the final character of two subsequent frames are equal, the second character is replaced with an /f/ if it is at the end of a frame, and an /a/ if it is at the end of a multiframe. insertion of alignment characters can be modified using the spi. the frame alignment character insertion (faci) is enabled by default. more information on the link controls is available in the memory map section, register 0x0571. 8-bit/10-bit encoder the 8-bit/10-bit encoder converts 8-bit octets into 10-bit symbols and inserts control characters into the stream when needed. the control characters used in jesd204b are shown in table 32. the 8-bit/10-bit encoding ensures that the signal is dc balanced by using the same number of ones and zeros across multiple symbols. the 8-bit/10-bit interface has options that can be controlled via the spi. these operations include bypass and invert. these options are intended to be troubleshooting tools for the verification of the digital front end (dfe). refer to the memory map section, register 0x0572, bits[2:1] for information on configuring the 8-bit/ 10-bit encoder. physical layer (driver) outputs digital outputs, timing, and controls the ad6684 physical layer consists of drivers that are defined in the jedec standard jesd204b, july 2011. the differential digital outputs are powered up by default. the drivers use a dynamic 100 internal termination to reduce unwanted reflections. place a 100 differential termination resistor at each receiver input to result in a nominal 300 mv p-p swing at the receiver (see figure 92). alternatively, single-ended 50 termination can be used. when single-ended termination is used, the termination voltage is drvdd1/2. otherwise, 0.1 f ac coupling capacitors can be used to terminate to any single- ended voltage. or serdoutx+ drvdd v rxcm serdoutx? output swing = 300mv p-p 0.1f 100? 50? 50? 0.1f receiver v cm = v rxcm 100? differential trace pair 14994-080 figure 92. ac-coupled digital output termination example table 32. ad6684 control characters used in jesd204b abbreviation control symbol 8-bit value 10-bit value, rd 1 = ?1 10-bit value, rd 1 = +1 description /r/ /k28.0/ 000 11100 001111 0100 110000 1011 start of multiframe /a/ /k28.3/ 011 11100 001111 0011 110000 1100 lane alignment /q/ /k28.4/ 100 11100 001111 0100 110000 1101 start of link configuration data /k/ /k28.5/ 101 11100 001111 1010 110000 0101 group synchronization /f/ /k28.7/ 111 11100 001111 1000 110000 0111 frame alignment 1 rd means running disparity.
ad6684 data sheet rev. 0 | page 58 of 107 the ad6684 digital outputs can interface with custom application specific integrated circuits (asics) and field programmable gate array (fpga) receivers, providing superior switching performance in noisy environments. single point to point network topologies are recommended with a single differential 100 termination resistor placed as close to the receiver inputs as possible. the common mode of the digital output automatically biases itself to half the drvdd1 supply of 1.25 v (v cm = 0.6 v). see figure 93 for an example of dc coupling the outputs to the receiver logic. serdoutx+ drvdd serdoutx? output swing = 300mv p-p 100 ? receiver v cm = drvdd/2 100 ? differential trace pair 14994-081 figure 93. dc-coupled digital output termination example if there is no far end receiver termination, or if there is poor differential trace routing, timing errors may result. to avoid such timing errors, it is recommended that the trace length be less than six inches, and that the differential output traces be close together and at equal lengths. figure 94, figure 95, and figure 96 show examples of the digital output data eye, time interval error (tie) jitter histogram, and bathtub curve, respectively, for one ad6684 lane running at 15 gbps. the format of the output data is twos complement by default. to change the output data format, see the memory map section (register 0x0561 in table 45 and table 46). de-emphasis de-emphasis enables the receiver eye diagram mask to be met in conditions where the interconnect insertion loss does not meet the jesd204b specification. use the preemphasis feature only when the receiver is unable to recover the clock due to excessive insertion loss. under normal conditions, preemphasis is disabled to conserve power. additionally, enabling and setting too high a preemphasis value on a short link can cause the receiver eye diagram to fail. use the preemphasis setting with caution because it can increase electromagnetic interference (emi). see the memory map section (registers 0x05c4 and register 0x05c6 in table 45 and table 46) for more details. phase-locked loop the phase-locked loop (pll) is used to generate the serializer clock, which operates at the jesd204b lane rate. the status of the pll lock can be checked in the pll lock status bit (register 0x056f, bit 7). this read only bit lets the user know if the pll has achieved a lock for the specific setup. the jesd204b lane rate control bit, bit 4 of register 0x056e, must be set to correspond with the lane rate. 500 ?500 ?300 ?200 ?100 0 100 200 300 ?60 ?40 ?20 0 20 40 60 voltage (mv) time (ps) 400 ?400 tx eye mask 14994-140 figure 94. ad6684 digital outputs data eye diagram; external 100 terminations at 15 gbps 16000 14000 12000 10000 8000 6000 4000 2000 0 ?4?20246 hits time (ps) 14994-141 figure 95. ad6684 digital outputs histogram; external 100 terminations at 15 gbps 1 1 ?2 1 ?4 1 ?6 1 ?8 1 ?10 1 ?12 1 ?16 1 ?14 ?0.5 ?0.4 ?0.3 ?0.2 ?0.1 0 0.1 0.2 0.3 0.4 0.5 ber ui 14994-142 figure 96. ad6684 digital outputs bathtub curve; external 100 terminations at 15 gbps
data sheet ad6684 rev. 0 | page 59 of 107 jesd204b tx converter mapping to support the different chip operating modes, the ad6684 design treats each sample stream (real or i/q) as originating from separate virtual converters. the i/q samples are always mapped in pairs with the i samples mapped to the first virtual converter and the q samples mapped to the second virtual converter. with this transport layer mapping, the number of virtual converters are the same whether ? a single real converter is used along with a digital downconverter block producing i/q outputs, or ? an analog downconversion is used with two real converters producing i/q outputs. figure 97 shows a block diagram of the two scenarios described for i/q transport layer mapping. the jesd204b tx block for ad6684 supports up to four ddc blocks. each ddc block outputs either two sample streams (i/q) for the complex data components (real + imaginary), or one sample stream for real (i) data. the jesd204b interface can be configured to use up to eight virtual converters depending on the ddc configuration. figure 98 shows the virtual converters and their relationship to the ddc outputs when complex outputs are used. table 33 shows the virtual converter mapping for each chip operating mode when channel swapping is disabled. real i q i converter 0 q converter 1 adc adc 90 phase jesd204b tx l lanes i/q analog mixing m = 2 adc real real i converter 0 q converter 1 jesd204b tx l lanes digital downconversion m = 2 digital downconversion 14994-084 figure 97. i/q transport layer mapping ddc 0 i q i q real/i converter 0 q converter 1 real/i real/q ddc 1 i q i q real/i converter 2 q converter 3 real/i real/q ddc 0 i q i q real/i converter 4 q converter 5 real/i real/q ddc 1 i q i q real/i converter 6 q converter 7 real/i real/q i/q crossbar mux i/q crossbar mux output interface output interface adc sampling at f s real/i adc sampling at f s real/q adc a sampling at f s real/i adc sampling at f s real/q 14994-085 figure 98. ddcs and virtual converter mapping
ad6684 data sheet rev. 0 | page 60 of 107 setting up the ad6684 digital interface the following spi writes are required for the ad6684 at startup and each time the adc is reset (datapath reset, soft reset, link power-down/power-up, or hard reset): 1. write 0x4f to register 0x1228. 2. write 0x0f to register 0x1228. 3. write 0x04 to register 0x1222. 4. write 0x00 to register 0x1222. 5. write 0x08 to register 0x1262. 6. write 0x00 to register 0x1262. the ad6684 has two jesd204b links. the device offers an easy way to set up the jesd204b link through the jesd04b quick configuration register (register 0x0570). the serial outputs (serdoutabx and serdoutcdx) are considered to be part of one jesd204b link. the basic parameters that determine the link setup are ? number of lanes per link (l) ? number of converters per link (m) ? number of octets per frame (f) if the internal ddcs are used for on-chip digital processing, m represents the number of virtual converters. the virtual converter mapping setup is shown in figure 98. the maximum lane rate allowed by the jesd204b specification is 15 gbps. the lane line rate is related to the jesd204b parameters using the following equation: lane line rate = l f nm out ? ? ? ? ? ? ? ?? 8 10 ' where: ratio decimation f f clock adc out _ ? the decimation ratio (dcm) is the parameter programmed in register 0x0201. use the following steps to configure the output: 1. power down the link. 2. select quick configuration options. 3. configure detailed options 4. set output lane mapping (optional). 5. set additional driver configuration options (optional). 6. power up the link. if the lane line rate calculated is less than 6.25 gbps, select the low line rate option by programming a value of 0x10 to register 0x056e. table 34 and table 35 show the jesd204b output configurations for both n? = 16 and n? = 8 for a given number of virtual converters. take care to ensure that the serial line rate for given configuration is within the supported range of 1.5625 gbps to 15 gbps. table 33. virtual converter mapping (per link) number of virtual converters supported chip application mode (register 0x0200, bits[3:0]) chip q ignore (register 0x0200, bit 5) virtual converter mapping 0 1 2 3 1 to 2 full bandwidth mode (0x0) real or complex (0x0) adc a/c samples adc b/d samples unused unused 1 one ddc mode (0x1) re al (i only) (0x1) ddc 0 i samples unused unused unused 2 one ddc mode (0x1) complex (i/q) (0x0) ddc 0 i samples ddc 0 q samples unused unused 2 two ddc mode (0x2) real (i only) (0x1) ddc 0 i samples ddc 1 i samples unused unused 4 two ddc mode (0x2) complex (i/q) (0x0) ddc 0 i samples ddc 0 q samples ddc 1 i samples ddc 1 q samples
data sheet ad6684 rev. 0 | page 61 of 107 table 34. jesd204b output configurations for n?= 16 number of virtual converters supported (same value as m) jesd204b quick configuration (0x0570) jesd204b serial line rate 1 jesd204b transport layer settings 2 l m f s hd n n? cs k 3 1 0x01 20 f out 1 1 2 1 0 8 to 16 16 0 to 3 only valid k values that are divisible by 4 are supported 0x40 10 f out 2 1 1 1 1 8 to 16 16 0 to 3 0x41 10 f out 2 1 2 2 0 8 to 16 16 0 to 3 2 0x0a 40 f out 1 2 4 1 0 8 to 16 16 0 to 3 0x49 20 f out 2 2 2 1 0 8 to 16 16 0 to 3 4 0x13 80 f out 1 4 8 1 0 8 to 16 16 0 to 3 0x52 40 f out 2 4 4 1 0 8 to 16 16 0 to 3 1 f out = output sample rate = adc sample rate/c hip decimation ratio. the jesd204b serial li ne rate must be 1687.5 mbps and 15,000 m bps. when the serial line rate is 15 gbps and 13.5 gbps, set bits[7:4] to 0x 3 in register 0x056e. when the serial line rate is 13. 5 gbps and 6.75 gbps, set b its[7:4] to 0x0 in re gister 0x056e. when the serial line rate is <6.75 gbps and 3 .375 gbps, set bits[7:4] to 0x1 in register 0x056e. when the serial line rate is 3.37 5 gbps and 1687.5 mbps, set bits[7:4] to 0x5 in register 0x056e. 2 jesd204b transport layer descriptions are as described in the jesd 204b overview section. 3 for f = 1, k = 20, 24, 28, and 32. for f = 2, k = 12, 16, 20, 24, 28, and 32. for f = 4, k = 8, 12, 16, 20, 24, 28, and 32. fo r f = 8 and f = 16, k = 4, 8, 12, 16, 20, 24, 28, and 32. table 35. jesd204b output configurations for n?= 8 number of virtual converters supported (same value as m) jesd204b quick configuration (register 0x0570) serial line rate 1 jesd204b transport layer settings 2 l m f s hd n n? cs k 3 1 0x00 10 f out 1 1 1 1 0 7 to 8 8 0 to 1 only valid k values which are divisible by 4 are supported 0x01 10 f out 1 1 2 2 0 7 to 8 8 0 to 1 0x40 5 f out 2 1 1 2 0 7 to 8 8 0 to 1 0x41 5 f out 2 1 2 4 0 7 to 8 8 0 to 1 0x42 5 f out 2 1 4 8 0 7 to 8 8 0 to 1 2 0x09 20 f out 1 2 2 1 0 7 to 8 8 0 to 1 0x48 10 f out 2 2 1 1 0 7 to 8 8 0 to 1 0x49 10 f out 2 2 2 2 0 7 to 8 8 0 to 1 1 f out = output sample rate = adc sample rate/c hip decimation ratio. the jesd204b serial li ne rate must be 1687.5 mbps and 15,000 m bps. when the serial line rate is 15 gbps and 13.5 gbps, set bits[7:4] to 0x 3 in register 0x056e. when the serial line rate is 13. 5 gbps and 6.75 gbps, set b its[7:4] to 0x0 in re gister 0x056e. when the serial line rate is <6.75 gbps and 3 .375 gbps, set bits[7:4] to 0x1 in register 0x056e. when the serial line rate is 3.37 5 gbps and 1687.5 mbps, set bits[7:4] to 0x5 in register 0x056e. 2 jesd204b transport layer descriptions are as described in the jesd 204b overview section. 3 for f = 1, k = 20, 24, 28, and 32. for f = 2, k = 12, 16, 20, 24, 28, and 32. for f = 4, k = 8, 12, 16, 20, 24, 28, and 32. fo r f = 8 and f = 16, k = 4, 8, 12, 16, 20, 24, 28, and 32.
ad6684 data sheet rev. 0 | page 62 of 107 example 1: adc with ddc option (two adcs plus two ddcs in each pair) the chip application mode is ddc mode (seefigure 99) with the following characteristics: ? chip application mode = two ddc mode (see figure 99) ? two 14-bit converters at 500 msps ? two ddc application layer mode with complex outputs (i/q) ? chip decimation ratio = 4 ? ddc decimation ratio = 4 (see table 33) the jesd204b output configuration is as follows: ? virtual converters required = 4 (see table 33) ? output sample rate (f out ) = 500/4 = 125 msps ? n? = 16 bits ? n = 16 bits ? l = 1, m = 4, and f = 8 (quick configuration = 0x13) ? cs = 0 to 1 ? k = 32 ? output serial line rate = 5 gbps per lane (l = 1) or 2.5 gbps per lane (l = 2) for l = 1, set bits[7:4] to 0x1 in register 0x056e. for l = 2, set bits[7:4] to 0x5 in register 0x056e. example 1 shows the flexibility in the digital and lane configurations for the ad6684 . the sample rate is 500 msps, but the outputs are all combined in either one or two lanes, depending on the i/o speed capability of the receiving device. nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 1 sysref real/i real/q real/i converter 2 q converter 3 i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 0 sysref real/i real/q real/i converter 0 q converter 1 l jesd204b lanes at up to 15gbps i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 1 sysref real/i real/q real/i converter 2 q converter 3 i q nco + mixer (optional) complex to real conversion (optional) hb4 fir dcm = bypass or 2 hb3 fir dcm = bypass or 2 hb2 fir dcm = bypass or 2 hb1 fir dcm = 2 gain = 0db or 6db ddc 0 sysref real/i real/q real/i converter 0 q converter 1 i q i/q crossbar mux i/q crossbar mux jesd204b transmit interface l jesd204b lanes at up to 15gbps jesd204b transmit interface adc sampling at f s real/i adc sampling at f s real/q adc sampling at f s real/i adc sampling at f s real/q synchronization control circuits sysref 14994-086 figure 99. two adc + four ddc mode in each pair
data sheet ad6684 rev. 0 | page 63 of 107 example 2: adc with nsr option (two adcs + nsr in each pair) the chip application mode is nsr mode (see figure 100) with the following characteristics: ? two 14-bit converters at 500 msps ? nsr blocks enabled for each channel ? chip decimation ratio = 1 the jesd204b output configuration is as follows: ? virtual converters required = 2 (see table 33). ? output sample rate (f out ) = 500 msps ? n? = 16 bits ? n = 9 bits ? l = 2, m = 2, and f = 2 (quick configuration = 0x49) ? cs = 0 to 2 ? k = 32 ? output serial lane rate = 10 gbps per lane (l = 2) ? set bits[7:4] to 0x0 in register 0x056e jesd204b transmit interface (jtx) 1 or 2 lanes real real converter 0 at 500msps at up to 15gbps nsr (21% or 28% bandwidth) 14-bit adc core at 500msps 14-bit adc core at 500msps 14-bit adc core at 500msps 14-bit adc core at 500msps real real converter 1 at 500msps nsr (21% or 28% bandwidth) converter 0 at 500msps nsr (21% or 28% bandwidth) converter 1 at 500msps nsr (21% or 28% bandwidth) jesd204b transmit interface (jtx) 1 or 2 lanes at up to 15gbps 14994-087 figure 100. two adc + nsr mode
ad6684 data sheet rev. 0 | page 64 of 107 latency end-to-end total latency tot a l l ate nc y i n t he ad6684 is dependent on the various digital signal processing (dsp) and jesd204b configuration modes. latency is fixed at 28 encode clocks through the adc itself, but the latency through the dsp and jesd204b blocks can vary greatly, depending on the configuration. therefore, the total latency must be calculated based on the dsp options selected and the jesd204b configuration. table 36 shows the combined latency through the adc, dsp, and jesd204b blocks for some of the different application modes supported by the ad6684 . latency is in units of the encode clock. table 36. latency through the ad6684 ? adc application mode jesd204b transport layer settings latency (number of encode clocks) l m f adc + dsp jesd204b total full bandwidth (9-bit) 2 2 2 30 14 44 ddc (hb1) 1 2 4 4 92 17 109 ddc (hb2 + hb1) 1 1 4 8 162 13 175 ddc (hb3 +hb2 + hb1) 1 1 4 8 292 28 320 ddc (hb4 + hb3 + hb2 + hb1) 1 1 4 8 548 39 587 decimate by 2 + nsr 1 2 4 64 6 70 nsr 2 2 2 38 16 54 1 no mixer, comp lex outputs.
data sheet ad6684 rev. 0 | page 65 of 107 multichip synchronization the ad6684 has a sysref input that provides flexible options for synchronizing the internal blocks. the sysref input is a source synchronous system reference signal that enables multichip synchronization. the input clock divider, ddcs, signal monitor block, and jesd204b link can be synchronized using the sysref input. for the highest level of timing accuracy, sysref must meet setup and hold requirements relative to the clk input. the flowchart in figure 101 describes the internal mechanism for multichip synchronization in the ad6684. the ad6684 supports several features that aid users in meeting the requirements set out for capturing a sysref signal. the sysref sample event can be defined as either a synchronous low to high transition, or a synchronous high to low transition. additionally, the ad6684 allows the sysref signal to be sampled using either the rising edge or falling edge of the clk input. the ad6684 also has the ability to ignore a programmable number (up to 16) of sysref events. the sysref control options can be selected using register 0x0120 and register 0x0121.
ad6684 data sheet rev. 0 | page 66 of 107 yes update setup/hold detector status (0x0128) increment sysref ignore counter yes no sysref enabled? (0x0120) no clock divider > 1? (0x010b) yes no input clock divider alignment required? yes no no yes align clock divider phase to sysref synchronization mode? (0x01ff) timestamp mode normal mode yes sysref inserted in jesd204b control bits back to start no ddc nco alignment enabled? (0x0300) yes no no yes send k28.5 characters normal jesd204b initialization sysref control bits? (0x0559, 0x055a, 0x058f) reset sysref ignore counter no start sysref asserted? yes no yes align signal monitor counters yes no no yes no increment sysref counter (0x012a) sysref timestamp delay (0x0123) back to start sysref ignore counter expired? (0x0121) clock divider auto adjust enabled? (0x0108) ramp test mode enabled? (0x0550) sysref resets ramp test mode generator jesd204b lmfc alignment required? align phase of all internal clocks (including lmfc) to sysref send invalid 8-bit/10-bit characters (all zeros) sync~ asserted signal monitor alignment enabled? (0x026f) align ddc nco phase accumulator 14994-088 figure 101. multichip synchronization
data sheet ad6684 rev. 0 | page 67 of 107 sysref setup/hold window monitor to ensure a valid sysref signal capture, the ad6684 has a sysref setup/hold window monitor. this feature allows the system designer to determine the location of the sysref signals relative to the clk signals by reading back the amount of setup/hold margin on the interface through the memory map. figure 102 and figure 103 show the setup and hold status values for different phases of sysref. the setup detector returns the status of the sysref signal before the clk edge, and the hold detector returns the status of the sysref signal after the clk edge. register 0x0128 stores the status of sysref and lets the user know if the sysref signal is captured by the adc. valid reg 0x0128[3:0] clk input sysref input flip flop hold (min) flip flop hold (min) flip flop setup (min) 0xf 0xe 0xd 0xc 0xb 0xa 0x9 0x8 0x7 0x6 0x5 0x4 0x3 0x2 0x1 0x0 14994-089 figure 102. sysref setup detector
ad6684 data sheet rev. 0 | page 68 of 107 clk input sysref input valid reg 0x0128[7:4] flip flop hold (min) flip flop hold (min) flip flop setup (min) 0xf 0xe 0xd 0xc 0xb 0xa 0x9 0x8 0x7 0x6 0x5 0x4 0x3 0x2 0x1 0x0 14994-090 figure 103. sysref hold detector table 37 shows the description of the contents of register 0x0128 and how to interpret them. table 37. sysref setup/hold monitor, register 0x0128 register 0x0128, bits[7:4] hold status register 0x0128, bits[3:0] setup status description 0x0 0x0 to 0x7 possible setup error. the smaller this number, the smaller the setup margin. 0x0 to 0x8 0x8 no setup or ho ld error (best hold margin). 0x8 0x9 to 0xf no setup or hold er ror (best setup and hold margin). 0x8 0x0 no setup or hold error (best setup margin). 0x9 to 0xf 0x0 possible hold error. the larger this number, the smaller the hold margin. 0x0 0x0 possible setup or hold error.
data sheet ad6684 rev. 0 | page 69 of 107 test modes adc test modes the ad6684 has various test options that aid in the system level implementation. the ad6684 has adc test modes that are available in register 0x0550. these test modes are described in table 38. when an output test mode is enabled, the analog section of the adc is disconnected from the digital back-end blocks, and the test pattern is run through the output formatting block. some of the test patterns are subject to output formatting, and some are not. the pn generators from the pn sequence tests can be reset by setting bit 4 or bit 5 of register 0x0550. these tests can be performed with or without an analog signal (if present, the analog signal is ignored); however, they do require an encode clock. if the application mode is set to select a ddc mode of operation, the test modes must be enabled for each ddc enabled. the test patterns can be enabled via bit 2 and bit 0 of register 0x0327, register 0x0347, depending on which ddc(s) are selected. the (i) data uses the test patterns selected for channel a, and the (q) data uses the test patterns selected for channel b. for more information, see the an-877 application note , interfacing to high speed adcs via spi . table 38. adc test modes output test mode bit sequence pattern name expression default/ seed value sample (n, n + 1, n + 2, ) 0000 off (default) not applicable not applicable not applicable 0001 midscale short 00 0000 0000 0000 not applicable not applicable 0010 +full-scale short 01 1111 1111 1111 not applicable not applicable 0011 ?full-scale short 10 0000 0000 0000 not applicable not applicable 0100 checkerboard 10 1010 1010 1010 not applicab le 0x1555, 0x2aaa, 0x1555, 0x2aaa, 0x1555 0101 pn sequence long x 23 + x 18 + 1 0x3aff 0x3fd7, 0x0002, 0x26e0, 0x0a3d, 0x1ca6 0110 pn sequence short x 9 + x 5 + 1 0x0092 0x125b, 0x3c9a, 0x2660, 0x0c65, 0x0697 0111 one word/zero word toggle 11 1111 1111 1111 not applicable 0x0000, 0x3fff, 0x0000, 0x3fff, 0x0000 1000 user input register 0x0551 to register 0x0558 not applicable user pattern 1[15:2], user pattern 2[15:2], user pattern 3[15:2], user pattern 4[15:2], user pattern 1[15:2] for repeat mode user pattern 1[15:2], user pattern 2[15:2], user pattern 3[15:2], user pattern 4[15:2], 0x0000 for single mode 1111 ramp output (x) % 2 14 not applicable (x) % 2 14 , (x +1) % 2 14 , (x +2) % 2 14 , (x +3) % 2 14
ad6684 data sheet rev. 0 | page 70 of 107 jesd204b block test modes in a ddition to t he adc pi peline te st modes, the ad6684 also has flexible test m odes in the jesd204b bloc k. these test modes are listed in register 0x0573 and register 0x0574. these test patterns can be injected at various points along the output data- path. these t est in jectio n points a re shown in figure 89. table 39 describes the various test mo des available in the jesd204b block. f or t he ad6684, a t ransition f rom te st modes (register 0x0573 0x00) to n orm al mode (register 0x0573 = 0x00) requir es an sp i soft reset. t his i s d one b y writing 0 x81 t o register 0x0000 (self cleared). transport layer sample test mode the transport layer samples are implemented in the ad6684 as defined by section 5.1.6.3 in the jedec jesd204b specification. these tests indicated by the value of register 0x0571, bit 5. the test pattern is equivalent to the raw samples from the adc. interface test modes the interface test modes are described in register 0x0573, bits[3:0]. these test modes are also explained in table 39. the interface tests can be injected at various points along the data. see figure 89 for more information on the test injection points. register 0x0573, bits[5:4] show where these tests are injected. table 40, table 41, and table 42 show examples of some of the test modes when injected at the jesd204b sample input, phy 10-bit input, and scrambler 8-bit input. in table 40, table 41, and table 42, upx represent the user pattern control bits from the customer register map. table 39. jesd204b interface test modes output test mode bit sequence pattern name expression default 0000 off (default) not appl icable not applicable 0001 alternating checker board 0x5555, 0xaaaa, 0x5555, not applicable 0010 1/0 word toggle 0x0000, 0xffff , 0x0000, not applicable 0011 31-bit pn sequence x 31 + x 28 + 1 0x0003afff 0100 23-bit pn sequence x 23 + x 18 + 1 0x003aff 0101 15-bit pn sequence x 15 + x 14 + 1 0x03af 0110 9-bit pn sequence x 9 + x 5 + 1 0x092 0111 7-bit pn sequence x 7 + x 6 + 1 0x07 1000 ramp output (x) % 2 16 ramp size depends on test injection point 1110 continuous/repeat user test register 0x0551 to register 0x0558 user pattern 1 to user pattern 4, then repeat 1111 single user test register 0x0551 to register 0x0558 user pattern 1 to user pattern 4, then zeros table 40. jesd204b sample input for m = 2, s = 2, n' = 16 (register 0x0573, bits[5:4] = 'b00) frame number converter number sample number alternating checkerboard 1/0 word toggle ramp 9-bit pn 23-bit pn user repeat user single 0 0 0 0x5555 0x0000 (x) % 2 16 0x496f 0xff5c up1[15:0] up1[15:0] 0 0 1 0x5555 0x0000 (x) % 2 16 0x496f 0xff5c up1[15:0] up1[15:0] 0 1 0 0x5555 0x0000 (x) % 2 16 0x496f 0xff5c up1[15:0] up1[15:0] 0 1 1 0x5555 0x0000 (x) % 2 16 0x496f 0xff5c up1[15:0] up1[15:0] 1 0 0 0xaaaa 0xffff (x +1) % 2 16 0xc9a9 0x0029 up2[15:0] up2[15:0] 1 0 1 0xaaaa 0xffff (x +1) % 2 16 0xc9a9 0x0029 up2[15:0] up2[15:0] 1 1 0 0xaaaa 0xffff (x +1) % 2 16 0xc9a9 0x0029 up2[15:0] up2[15:0] 1 1 1 0xaaaa 0xffff (x +1) % 2 16 0xc9a9 0x0029 up2[15:0] up2[15:0] 2 0 0 0x5555 0x0000 (x +2) % 2 16 0x980c 0xb80a up3[15:0] up3[15:0] 2 0 1 0x5555 0x0000 (x +2) % 2 16 0x980c 0xb80a up3[15:0] up3[15:0] 2 1 0 0x5555 0x0000 (x +2) % 2 16 0x980c 0xb80a up3[15:0] up3[15:0] 2 1 1 0x5555 0x0000 (x +2) % 2 16 0x980c 0xb80a up3[15:0] up3[15:0] 3 0 0 0xaaaa 0xffff (x +3) % 2 16 0x651a 0x3d72 up4[15:0] up4[15:0] 3 0 1 0xaaaa 0xffff (x +3) % 2 16 0x651a 0x3d72 up4[15:0] up4[15:0] 3 1 0 0xaaaa 0xffff (x +3) % 2 16 0x651a 0x3d72 up4[15:0] up4[15:0] 3 1 1 0xaaaa 0xffff (x +3) % 2 16 0x651a 0x3d72 up4[15:0] up4[15:0] 4 0 0 0x5555 0x0000 (x +4) % 2 16 0x5fd1 0x9b26 up1[15:0] 0x0000 4 0 1 0x5555 0x0000 (x +4) % 2 16 0x5fd1 0x9b26 up1[15:0] 0x0000 4 1 0 0x5555 0x0000 (x +4) % 2 16 0x5fd1 0x9b26 up1[15:0] 0x0000 4 1 1 0x5555 0x0000 (x +4) % 2 16 0x5fd1 0x9b26 up1[15:0] 0x0000
data sheet ad6684 rev. 0 | page 71 of 107 table 41. physical layer 10-bit inpu t (register 0x0573, bits[5:4] = 'b01) 10-bit symbol number alternating checkerboard 1/0 word toggle ramp 9-bit pn 23-bit pn user repeat user single 0 0x155 0x000 (x) % 2 10 0x125 0x3fd up1[15:6] up1[15:6] 1 0x2aa 0x3ff (x + 1) % 2 10 0x2fc 0x1c0 up2[15:6] up2[15:6] 2 0x155 0x000 (x + 2) % 2 10 0x26a 0x00a up3[15:6] up3[15:6] 3 0x2aa 0x3ff (x + 3) % 2 10 0x198 0x1b8 up4[15:6] up4[15:6] 4 0x155 0x000 (x + 4) % 2 10 0x031 0x028 up1[15:6] 0x000 5 0x2aa 0x3ff (x + 5) % 2 10 0x251 0x3d7 up2[15:6] 0x000 6 0x155 0x000 (x + 6) % 2 10 0x297 0x0a6 up3[15:6] 0x000 7 0x2aa 0x3ff (x + 7) % 2 10 0x3d1 0x326 up4[15:6] 0x000 8 0x155 0x000 (x + 8) % 2 10 0x18e 0x10f up1[15:6] 0x000 9 0x2aa 0x3ff (x + 9) % 2 10 0x2cb 0x3fd up2[15:6] 0x000 10 0x155 0x000 (x + 10) % 2 10 0x0f1 0x31e up3[15:6] 0x000 11 0x2aa 0x3ff (x + 11) % 2 10 0x3dd 0x008 up4[15:6] 0x000 table 42. scrambler 8-bit input (register 0x0573, bits[5:4] = 'b10) 8-bit octet number alternating checkerboard 1/0 word toggle ramp 9-bit pn 23-bit pn user repeat user single 0 0x55 0x00 (x) % 2 8 0x49 0xff up1[15:9] up1[15:9] 1 0xaa 0xff (x + 1) % 2 8 0x6f 0x5c up2[15:9] up2[15:9] 2 0x55 0x00 (x + 2) % 2 8 0xc9 0x00 up3[15:9] up3[15:9] 3 0xaa 0xff (x + 3) % 2 8 0xa9 0x29 up4[15:9] up4[15:9] 4 0x55 0x00 (x + 4) % 2 8 0x98 0xb8 up1[15:9] 0x00 5 0xaa 0xff (x + 5) % 2 8 0x0c 0x0a up2[15:9] 0x00 6 0x55 0x00 (x + 6) % 2 8 0x65 0x3d up3[15:9] 0x00 7 0xaa 0xff (x + 7) % 2 8 0x1a 0x72 up4[15:9] 0x00 8 0x55 0x00 (x + 8) % 2 8 0x5f 0x9b up1[15:9] 0x00 9 0xaa 0xff (x + 9) % 2 8 0xd1 0x26 up2[15:9] 0x00 10 0x55 0x00 (x + 10) % 2 8 0x63 0x43 up3[15:9] 0x00 11 0xaa 0xff (x + 11) % 2 8 0xac 0xff up4[15:9] 0x00 data link layer test modes the data link layer test modes are implemented in the ad6684 as defined by section 5.3.3.8.2 in the jedec jesd204b specification. these tests are shown in register 0x0574, bits[2:0]. test patterns inserted at this point are useful for verifying the functionality of the data link layer. when the data link layer test modes are enabled, disable syncinbab/syncinbcd by writing 0xc0 to register 0x0572.
ad6684 data sheet rev. 0 | page 72 of 107 serial port interface the ad6684 spi allows the user to configure the converter for specific functions or operations through a structured register space provided inside the adc. the spi gives the user added flexibility and customization, depending on the application. addresses are accessed via the serial port and can be written to or read from the port. memory is organized into bytes that can be further divided into fields. these fields are documented in the memory map section. for detailed operational information, see the serial control interface standard (rev. 1.0) . configuration using the spi three pins define the spi of this adc: the sclk pin, the sdio pin, and the csb pin (see table 43). the sclk (serial clock) pin is used to synchronize the read and write data presented from and to the adc. the sdio (serial data input/output) pin is a dual-purpose pin that allows data to be sent and read from the internal adc memory map registers. the csb (chip select bar) pin is an active low control that enables or disables the read and write cycles. table 43. serial port interface pins pin function sclk serial clock. the serial shift clock input, which is used to synchronize serial interface reads and writes. sdio serial data inp ut/output. a dual-purpose pin that typically serves as an input or an output, depending on the instruction being sent and the relative position in the timing frame. csb chip select bar. an active low control that gates the read and write cycles. the falling edge of csb, in conjunction with the rising edge of sclk, determines the start of the framing. an example of the serial timing and its definitions can be found in figure 4 and table 5. other modes involving the csb pin are available. the csb pin can be held low indefinitely, which permanently enables the device; this is called streaming. the csb can stall high between bytes to allow for additional external timing. when csb is tied high, spi functions are placed in a high impedance mode. this mode turns on the secondary functions of the spi pin. all data is composed of 8-bit words. the first bit of each individual byte of serial data indicates whether a read or write command is issued. this bit allows the sdio pin to change direction from an input to an output. in addition to word length, the instruction phase determines whether the serial frame is a read or write operation, allowing the serial port to be used both to program the chip and to read the contents of the on-chip memory. if the instruction is a readback operation, performing a readback causes the sdio pin to change direction from an input to an output at the appropriate point in the serial frame. data can be sent in msb first mode or in lsb first mode. msb first mode is the default on power-up and can be changed via the spi port configuration register. for more information about this and other features, see the serial control interface standard (rev. 1.0) . hardware interface the pins described in table 43 comprise the physical interface between the user programming device and the serial port of the ad6684 . the sclk pin and the csb pin function as inputs when using the spi interface. the sdio pin is bidirectional, functioning as an input during write phases and as an output during readback. the spi interface is flexible enough to be controlled by either fpgas or microcontrollers. one method for spi configuration is described in detail in the an-812 application note , microcontroller-based serial port interface (spi) boot circuit . do not activate the spi port during periods when the full dynamic performance of the converter is required. because the sclk signal, the csb signal, and the sdio signal are typically asynchronous to the adc clock, noise from these signals can degrade converter performance. if the on-board spi bus is used for other devices, it may be necessary to provide buffers between this bus and the ad6684 to prevent these signals from transitioning at the converter inputs during critical sampling periods. spi accessible features table 44 provides a brief description of the general features that are accessible via the spi. these features are described in detail in the serial control interface standard (rev. 1.0) . the ad6684 device specific features are described in the memory map section. table 44. features accessible using the spi feature name description mode allows the user to set either power-down mode or standby mode. clock allows the user to access the clock divider via the spi. ddc allows the user to set up decimation filters for different applications. test input/output allows the user to set test modes to have known data on output bits. output mode allows the user to set up outputs. serdes output setup allows the user to vary serdes settings such as swing and emphasis.
data sheet ad6684 rev. 0 | page 73 of 107 memory map reading the memory map register table each row in the memory map register table has eight bit locations. the memory map is divided into four sections: the analog devices spi registers (register 0x0000 to register 0x000d and register 0x18a6 to register 0x1a4d), the adc function registers (register 0x003f to register 0x027a), the ddc, nsr, and vdr function registers (register 0x0300 to register 0x0434), and the digital outputs and test modes registers (register 0x0550 to register 0x05c6). table 45 documents the default hexadecimal value for each hexadecimal address shown. the column with the heading bit 7 (msb) is the start of the default hexadecimal value given. for example, address 0x0561, the output mode register, has a hexadecimal default value of 0x01. this means that bit 0 = 1, and the remaining bits are 0s. this setting is the default output format value, which is twos complement. for more information on this function and others, see table 45 and table 46. open and reserved locations all address and bit locations that are not included in table 45 are not currently supported for this device. write unused bits of a valid address location with 0s unless the default value is set otherwise. writing to these locations is required only when part of an address location is unassigned (for example, address 0x0561). if the entire address location is open (for example, address 0x0013), do not write to this address location. default values after the ad6684 is reset, critical registers are loaded with default values. the default values for the registers are given in the memory map register table, table 45. logic levels an explanation of logic level terminology follows: ? bit is set is synonymous with bit is set to logic 1 or writing logic 1 for the bit. ? clear a bit is synonymous with bit is set to logic 0 or writing logic 0 for the bit. ? x denotes a dont care bit. adc pair addressing the ad6684 functionally operates as two pairs of dual if receiver channels. there are two adcs, two nsr processing blocks, two vdr processing blocks, and two ddcs in each pair, resulting in a total of four of each for the ad6684 . to access the spi registers for each pair, the pair index must be written in register 0x0009. the pair index regist must be written prior to any other spi write to the ad6684 . channel-specific registers some channel setup functions, such as the fast detect control (register 0x0247), can be programmed to a different value for each channel. in these cases, channel address locations are internally duplicated for each channel. these registers and bits are designated in table 45 as local. these local registers and bits can be accessed by setting the appropriate channel a/channel c or channel b/channel d bits in register 0x0008. the particular channel that is addressed is dependent upon the pair selection written to register 0x0009. if both bits are set, the subsequent write affects the registers of both channels. in a read cycle, set only channel a/channel c or channel b/channel d to read one of the two registers. if both bits are set during an spi read cycle, the device returns the value for channel a. if both pairs and both channels have been selected via register 0x0009 and register 0x0008, then the device returns the value for channel a. the names of the registers listed in table 45 and table 46 are prefixed with either global map, channel map, jesd204b map, or pair map. registers in the pair map and jesd204b map apply to a pair of channels, either pair a/b or pair c/d. to write registers in the pair map and the jesd204b map, the pair index register (register 0x0009) must be written to address the appropriate pair. the spi configuration a (register 0x0000), spi config- uration b (register 0x0001), and pair index (register 0x0009) registers are the only registers that reside in the global map. registers in the channel map are local to each channel, either channel a, channel b, channel c, or channel d. to write registers in the channel map, the pair index register (register 0x0009) must be written first to address the desired pair (pair a/b or pair c/d), followed by writing the channel index register (register 0x0008) to select the desired channel (channel a/channel c or channel b/ channel d). for example, to write channel a to a test mode (set by register 0x0550), first write a value of 0x01 to register 0x0009 to select pair a/b, followed by writing 0x01 to register 0x0008 to select channel a. then, write register 0x0550 to the value for the desired test mode. to write all channels to a test mode (set by register 0x0550), first write register 0x0009 to a value of 0x03 to select both pair a/b and pair c/d, followed by writing register 0x0008 to a value of 0x03 to select channel a, channel b, channel c, and channel d. next, write register 0x0550 to the value for the desired test mode. spi soft reset after issuing a soft reset by programming 0x81 to register 0x0000, the ad6684 requires 5 ms to recover. when programming the ad6684 for application setup, ensure that an adequate delay is programmed into the firmware after asserting the soft reset and before starting the device setup.
ad6684 data sheet rev. 0 | page 74 of 107 memory map memory map summary all address locations that are not included in table 45 are not currently supported for this device and must not be written. table 45. memory map summary reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x0000 global map spi configuratio n a soft reset (self clearing) lsb first mirror address ascension mirror reserved address ascension lsb first soft reset (self clearing) 0x00 r/w 0x0001 global map spi config- uration b single instruction reserved datapath soft reset (self clearing) reserved 0x00 r/w 0x0002 channel map chip config- uration reserved channel po wer modes 0x00 r/w 0x0003 pair map chip type chip_type 0x03 r 0x0004 pair map chip id lsb chip_id[7:0] 0xdc r 0x0006 pair map chip grade chip_speed_grade reserved 0x00 r 0x0008 pair map device index reserved channel b/ channel d channel a/chan- nel c 0x03 r/w 0x0009 global map pair index reserved pair c/d pair a/b 0x03 r/w 0x000a pair map scratch pad scratch pad 0x07 r/w 0x000b pair map spi revision spi_revision 0x01 r 0x000c pair map vendor id lsb chip_vendor_id[7:0] 0x56 r 0x000d pair map vendor id msb chip_vendor_id[15:8] 0x04 r 0x003f channel map chip power- down pin pdwn/ stby disable reserved 0x00 r/w 0x0040 pair map chip pin control 1 pdwn/stby function fast detect b/fast detect d (fd_b/fd_d) fast detect a/fast detect c (fd_a/fd_c) 0x3f r/w 0x0108 pair map clock divider control reserved clock divider 0x01 r/w 0x0109 channel map clock divider phase reserved clock divider phase offset 0x00 r/w 0x010a pair map clock divider sysref control clock divider auto phase adjust reserved clock divider negative skew window clock divider positive skew window 0x00 r/w 0x0110 pair map clock delay control reserved clock delay mode select 0x00 r/w 0x0111 channel map clock super fine delay clock super fine delay adjust 0x00 r/w 0x0112 channel map clock fine delay clock fine delay adjust 0xc0 r/w
data sheet ad6684 rev. 0 | page 75 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x011a clock detection control reserved clock detection threshold clock detection enable reserved 0x00 r/w 0x011b pair map clock status reserved input clock detect 0x00 r 0x011c clock dcs control reserved clock dcs enable clock dcs power- up 0x00 r/w 0x0120 pair map sysref control 1 reserved sysref flag reset reserved sysref transition select clk edge select sysref mode select reserved 0x00 r/w 0x0121 pair map sysref control 2 reserved sysref n shot igno re counter select 0x00 r/w 0x0123 pair map sysref control 4 reserved sysref time stamp delay[6:0] 0x40 r/w 0x0128 pair map sysref status 1 sysref hold status[7:4] sysref setup status[3:0] 0x00 r 0x0129 pair map sysref status 2 reserved clock divider phase when sysref is captured 0x00 r 0x012a pair map sysref status 3 sysref counter [7:0] (increments when a sysref input is captured) 0x00 r 0x01ff pair map chip sync reserved synchro- nization mode 0x00 r/w 0x0200 pair map chip mode reserved chip q ignore reserved chip application mode 0x07 r/w 0x0201 pair map chip decim- ation ratio reserved chip decimation ratio select 0x00 r/w 0x0228 channel map custom offset offset adjust in lsbs from +127 to ?128 0x00 r/w 0x0245 channel map fast detect control reserved force fd_a/ fd_b/ fd_c/ fd_d pins force value of fd_a/fd_b/ fd_c/fd_d pins; if force pins is true, this value is output on the fd_x pins reserved enable fast detect output 0x00 r/w 0x0247 channel map fast detect upper threshold lsb fast detect upper threshold[7:0] 0x00 r/w 0x0248 channel map fast detect upper threshold msb reserved fast detect uppe r threshold[12:8] 0x00 r/w 0x0249 channel map fast detect lower threshold lsb fast detect lower threshold[7:0] 0x00 r/w 0x024a channel map fast detect lower threshold msb reserved fast detect lower threshold[12:8] 0x00 r/w
ad6684 data sheet rev. 0 | page 76 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x024b channel map fast detect dwell time lsb fast detect dwell time[7:0] 0x00 r/w 0x024c channel map fast detect dwell time msb fast detect dwell time[15:8] 0x00 r/w 0x026f pair map signal monitor sync control reserved signal monitor synchro- nization mode 0x00 r/w 0x0270 channel map signal monitor control reserved peak detector reserved 0x00 r/w 0x0271 channel map signal monitor period 0 signal monitor period[7:0] 0x80 r/w 0x0272 channel map signal monitor period 1 signal monitor period[15:8] 0x00 r/w 0x0273 channel map signal monitor period 2 signal monitor period[23:16] 0x00 r/w 0x0274 channel map signal monitor status control reserved result update reserved result selection 0x01 r/w 0x0275 channel map signal monitor status 0 signal monitor result[7:0] 0x00 r 0x0276 channel map signal monitor status 1 signal monitor result[15:8] 0x00 r 0x0277 channel map signal monitor status 2 reserved signal monitor result[19:16] 0x00 r 0x0278 channel map signal monitor status frame counter period count result, bits[7:0] 0x00 r 0x0279 channel map signal monitor serial framer control reserved signal monitor sport over jes- d204b enable 0x00 r/w 0x027a channel map signal monitor serial framer input selection reserved signal monitor sport over je sd204b peak detector enable 0x02 r/w 0x0300 pair map ddc sync control reserved ddc nco soft reset reserved ddc next sync ddc synchro- nization mode 0x00 r/w
data sheet ad6684 rev. 0 | page 77 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x0310 pair map ddc 0 control ddc 0 mixer select ddc 0 gain select ddc 0 if mode ddc 0 complex to real enable reserved ddc 0 decimation rate select 0x00 r/w 0x0311 pair map ddc 0 input select reserved ddc 0 q input select reserved ddc 0 i input select 0x00 r/w 0x0314 pair map ddc 0 phase increment 0 ddc 0 nco frequency value, twos complement[7:0] 0x00 r/w 0x0315 pair map ddc 0 phase increment 1 ddc 0 nco frequency value, twos complement[15:8] 0x00 r/w 0x0316 pair map ddc 0 phase increment 2 ddc 0 nco frequency value, twos complement[23:16] 0x00 r/w 0x0317 pair map ddc 0 phase increment 3 ddc 0 nco frequency value, twos complement[31:24] 0x00 r/w 0x0318 pair map ddc 0 phase increment 4 ddc 0 nco frequency value, twos complement[39:32] 0x00 r/w 0x031a pair map ddc 0 phase increment 5 ddc 0 nco frequency value, twos complement[47:40] 0x00 r/w 0x031d pair map ddc 0 phase offset 0 ddc 0 nco phase value, twos complement[7:0] 0x00 r/w 0x031e pair map ddc 0 phase offset 1 ddc 0 nco phase value, twos complement[15:8] 0x00 r/w 0x031f pair map ddc 0 phase offset 2 ddc 0 nco phase value, twos complement[23:16] 0x00 r/w 0x0320 pair map ddc 0 phase offset 3 ddc 0 nco phase value, twos complement[31:24] 0x00 r/w 0x0321 pair map ddc 0 phase offset 4 ddc 0 nco phase value, twos complement[39:32] 0x00 r/w 0x0322 pair map ddc 0 phase offset 5 ddc 0 nco phase value, twos complement[47:40] 0x00 r/w 0x0327 pair map ddc 0 test enable reserved ddc 0 q output test mode enable reserved ddc 0 i output test mode enable 0x00 r/w 0x0330 pair map ddc 1 control ddc 1 mixer select ddc 1 gain select ddc 1 if mode ddc 1 complex to real enable reserved ddc 1 decimation rate select 0x00 r/w 0x0331 pair map ddc 1 input select reserved ddc 1 q input select reserved ddc 1 i input select 0x05 r/w 0x0334 pair map ddc 1 phase increment 0 ddc 1 nco frequency value, twos complement[7:0] 0x00 r/w 0x0335 pair map ddc 1 phase increment 1 ddc 1 nco frequency value, twos complement[15:8] 0x00 r/w 0x0336 pair map ddc 1 phase increment 2 ddc 1 nco frequency value, twos complement[23:16] 0x00 r/w
ad6684 data sheet rev. 0 | page 78 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x0337 pair map ddc 1 phase increment 3 ddc 1 nco frequency value, twos complement[31:24] 0x00 r/w 0x0338 pair map ddc 1 phase increment 4 ddc 1 nco frequency value, twos complement[39:32] 0x00 r/w 0x033a pair map ddc 1 phase increment 5 ddc 1 nco frequency value, twos complement[47:40] 0x00 r/w 0x033d pair map ddc 1 phase offset 0 ddc 1 nco phase value, twos complement[7:0] 0x00 r/w 0x033e pair map ddc 1 phase offset 1 ddc 1 nco phase value, twos complement[15:8] 0x00 r/w 0x033f pair map ddc 1 phase offset 2 ddc 1 nco phase value, twos complement[23:16] 0x00 r/w 0x0340 pair map ddc 1 phase offset 3 ddc 1 nco phase value, twos complement[31:24] 0x00 r/w 0x0341 pair map ddc 1 phase offset 4 ddc 1 nco phase value, twos complement[39:32] 0x00 r/w 0x0342 pair map ddc 1 phase offset 5 ddc 1 nco phase value, twos complement[47:40] 0x00 r/w 0x0347 pair map ddc 1 test enable reserved ddc 1 q output test mode enable reserved ddc 1 i output test mode enable 0x00 r/w 0x041e channel map nsr dec- imate by 2 control high-pass/ low-pass mode reserved nsr dec- imate by 2 enable 0x00 r/w 0x0420 nsr mode reserved nsr mode reserved 0x00 r/w 0x0422 channel map nsr tuning reserved nsr tuning word 0x00 r/w 0x0430 pair map vdr control reserved vdr bandwidth vdr complex mode enable 0x01 r/w 0x0434 channel map vdr tuning frequency reserved vdr center frequency 0x00 r/w 0x0550 channel map test mode control user pattern selection reser- ved reset pn sequence reset pn short generation test mode selection 0x00 r/w 0x0551 pair map user pattern 1 lsb user pattern 1[7:0] 0x00 r/w 0x0552 pair map user pattern 1 msb user pattern 1[15:8] 0x00 r/w 0x0553 pair map user pattern 2 lsb user pattern 2[7:0] 0x00 r/w 0x0554 pair map user pattern 2 msb user pattern 2[15:8] 0x00 r/w
data sheet ad6684 rev. 0 | page 79 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x0555 pair map user pattern 3 lsb user pattern 3[7:0] 0x00 r/w 0x0556 pair map user pattern 3 msb user pattern 3[15:8] 0x00 r/w 0x0557 pair map user pattern 4 lsb user pattern 4[7:0] 0x00 r/w 0x0558 pair map user pattern 4 msb user pattern 4[15:8] 0x00 r/w 0x0559 pair map output control mode 0 reserved converter control bit 1 selection rese rved converter control bit 0 selection 0x00 r/w 0x055a pair map output control mode 1 reserved converter control bit 2 selection 0x01 r/w 0x0561 pair map ou tput sample mode reserved sample invert data format select 0x01 r/w 0x0564 pair map output channel select reserved reserved con- verter channel swap control 0x00 r/w 0x056e jesd204b map pll control jesd204b lane rate control reserved 0x00 r/w 0x056f jesd204b map pll status pll lock status reserved 0x00 r 0x0570 jesd204b map jtx quick configuration quick configuration l quick configuration m quick configuration f 0x49 r/w 0x0571 jesd204b map jtx link control 1 standby mode tail bit (t) pn long transport layer test lane synchronization ilas sequence mode faci link control 0x14 r/w 0x0572 jesd204b map jtx link control 2 syncinbab/ syncinbcd pin control sync- inbab/ syncinbcd pin invert syncinbab/ syncinbcd pin type reserved 8-bit/10-bit bypass 8-bit/10-bit invert reserved 0x00 r/w 0x0573 jesd204b map jtx link control 3 checksum mode test injection point jesd204b test mode patterns 0x00 r/w 0x0574 jesd204b map jtx link control 4 ilas delay reserved link layer test mode 0x00 r/w 0x0578 jesd204b map jtx lmfc offset reserved lmfc phase offset value 0x00 r/w 0x0580 jesd204b map jtx did configuration jesd204b tx serial device identification (did) value 0x00 r/w 0x0581 jesd204b map jtx bid configuration reserved jesd204b tx serial bank identification (bid) value 0x00 r/w 0x0583 jesd204b map jtx lid 0 configuration reserved lane 0 serial lane identification (lid) value 0x00 r/w
ad6684 data sheet rev. 0 | page 80 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x0585 jesd204b map jtx lid 1 configuration reserved lane 1 lid value 0x02 r/w 0x058b jesd204b map jtx scr l configuration jesd204b scrambling (scr) reserved jesd204b lanes (l) 0x81 r/w 0x058c jesd204b map jtx f configuration number of octets per frame (f) 0x01 r 0x058d jesd204b map jtx k configuration reserved number of frames per multiframe (k) 0x1f r/w 0x058e jesd204b map jtx m configuration number of converters per link 0x01 r 0x058f jesd204b map jtx cs n configuration number of control bits (cs) per sample reserved adc converter resolution (n) 0x0f r/w 0x0590 jesd204b map jtx subclass version np configuration subclass support adc number of bits per sample (n') 0x2f r/w 0x0591 jesd204b map jtx jv s configuration reserved samples per converter frame cycle (s) 0x20 r 0x0592 jesd204b map jtx hd cf configuration hd value reserved control words per frame clock cycle per link (cf) 0x00 r 0x05a0 jesd204b map jtx checksum 0 configuration checksum 0 checksum value for serdoutab0/serdoutcd0 0xc3 r 0x05a1 jesd204b map jtx checksum 1 configuration checksum 1 checksum value for serdoutab1/serdoutcd1 0xc4 r 0x05b0 jesd204b map jtx lane power-down reserved jesd204b lane 1 power-down reserved jesd- 204b lane 0 power- down 0xfa r/w 0x05b2 jesd204b map jtx lane assign- ment 1 reserved serdoutab0/serdoutcd0 lane assignment 0x00 r/w 0x05b3 jesd204b map jtx lane assign- ment 2 reserved serdoutab1/serdoutcd1 lane assignment 0x11 r/w 0x05c0 jesd204b map jesd204b serializer drive adjust reserved swing voltage for serdoutab1/ serdoutcd1 reserved swing voltage for serdoutab0/ serdoutcd0 0x11 r/w 0x05c4 jesd204b serializer preemph- asis selection register for logical lane 0 post tab polarity sets post tab level pretab polarty sets pretab level 0x0 r/w
data sheet ad6684 rev. 0 | page 81 of 107 reg. name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 reset r/w 0x05c6 jesd204b serializer preempha- sis selection register for logical lane 0 post tab polarity sets post tab level pre tab polarty sets pre tab level 0x0 r/w 0x0922 large dither control large dither control 0x70 r/w 0x1222 pll calibration pll calibration 0x0 r/w 0x1228 jesd204b start-up circuit reset jesd204b start-up ci rcuit reset 0xf r/w 0x1262 pll loss of lock control pll loss of lock control 0x0 r/w 0x18a6 pair map vref control reserved vre f control 0x00 r/w 0x18e0 external vcm buffer control 1 external vcm buffer control 1 0x00 r/w 0x18e1 external vcm buffer control 2 external vcm buffer control 1 0x00 r/w 0x18e2 external vcm buffer control 3 external vcm buffer control 1 0x00 r/w 0x18e3 external vcm buffer control reserved external vcm buffe r external vcm buffer current setting 0x00 r/w 0x18e6 temp- erature diode export reserv ed t emp- erature diode export 0x00 r/w 0x1908 channel map analog input control reserved analog input dc coupling selection reserved 0x00 r/ w 0x1910 channel map input full- scale range reserved input full-scale control 0x 0d r/ w 0x1a4c channel map buffer control 1 reserved buffer control 1 0x0c r/w 0x1a4d channel map buffer control 2 reserved buffer control 2 0x0c r/w
ad6684 data sheet rev. 0 | page 82 of 107 memory map details all address locations that are not included in table 46 are not currently supported for this device and must not be written. table 46. memory map details address name bits bit name settings description reset access 0x0000 global map spi config- uration a 7 soft reset (self clearing) when a soft reset is issued, the user must wait 5 ms before writing to any other register. this wait provides sufficient time for the boot loader to complete. 0x0 r/w 0 do nothing. 1 reset the spi and registers (self clearing). 6 lsb first mirror 0x0 r/w 1 lsb shifted first for all spi operations. 0 msb shifted first for all spi operations. 5 address ascension mirror 0x0 r/w 0 multibyte spi operations cause addresses to auto-increment. 1 multibyte spi operations cause addresses to auto-increment. [4:3] reserved reserved. 0x0 r 2 address ascension 0x0 r/w 0 multibyte spi operations cause addresses to autoincrement. 1 multibyte spi operations cause addresses to auto increment. 1 lsb first 0x0 r/w 1 lsb shifted first for all spi operations. 0 msb shifted first for all spi operations. 0 soft reset (self clearing) when a soft reset is issued, the user must wait 5 ms before writing to any other register. this wait provides sufficient time for the boot loader to complete. 0x0 r/w 0 do nothing. 1 reset the spi and registers (self clearing). 0x0001 global map spi config- uration b 7 single instruction 0x0 r/w 0 spi streaming enabled. 1 streaming (multibyte read/write) is disabled. only one read or write operation is performed, regardless of the state of the csb line. [6:2] reserved reserved. 0x0 r 1 datapath soft reset (self clearing) 0x0 r/w 0 normal operation. 1 datapath soft re set (self-clearing). 0 reserved reserved. 0x0 r 0x0002 channel map chip config- uration [7:2] reserved reserved. 0x0 r [1:0] channel power modes channel power modes. 0x0 r/w 00 normal mode (power up). 10 standby mode. the digital datapath clocks are disabled, the jesd204b interface is enabled, and the outputs are enabled. 11 power-down mode. the digital datapath clocks are disabled, th e digital datapath is held in reset, the jesd204b interface is disabled, and the outputs are disabled.
data sheet ad6684 rev. 0 | page 83 of 107 address name bits bit name settings description reset access 0x0003 pair map chip type [7:0] chip_type chip type. 0x3 r 0x3 high speed adc. 0x0004 pair map chip id lsb [7:0] chip_id chip id. 0xdc r 0x0006 pair map chip grade [7:4] chip_speed_grade chip speed grade. 0x0 r 0101 500 mhz. [3:0] reserved reserved. 0x0 r 0x0008 pair map device index [7:2] reserved reserved. 0x0 r 1 channel b/channel d 0x1 r/w 0 adc core b/adc core d does not receive the next spi command. 1 adc core b/adc core d receives the next spi command. 0 channel a/channel c 0x1 r/w 0 adc core a/adc core c does not receive the next spi command. 1 adc core a/adc core c receives the next spi command. 0x0009 global map pair index [7:2] reserved reserved. 0x0 r 1 pair c/d 0x1 r/w 0 adc pair c/d does not receive the next read/ write command from the spi interface. 1 adc pair c/d does not receive the next read/ write command from the spi interface. 0 pair a/b 0x1 r/w 0 adc pair a/b does not receive the next read/ write command from the spi interface. 1 adc pair a/b receives the next read/write command from the spi interface. 0x000a pair map scratch pad [7:0] scratch pad chip scratch pad register. this register provides a consistent memory location for software debug. 0x07 r/w 0x000b pair map spi revision [7:0] spi_revision spi revision register (0x01 = revision 1.0). 0x1 r 00000001 revision 1.0. 0x000c pair map vendor id lsb [7:0] chip_vendor_id[7:0] vendor id. 0x56 r 0x000d pair map vendor id msb [7:0] chip_vendor_id[15:8] vendor id. 0x4 r 0x003f channel map chip power- down pin 7 pdwn/stby disable this bit is used in conjunction with register 0x0040. 0x0 r/w 0 power-down pin (pdwn/stby) enabled; global pin control selection enabled (default). 1 power-down pin (pdwn/stby) disabled/ ignored; global pin control selection ignored. [6:0] reserved reserved. 0x0 r
ad6684 data sheet rev. 0 | page 84 of 107 address name bits bit name settings description reset access 0x0040 pair map chip pin control 1 [7:6] pdwn/stby function 0x0 r/w 00 power-down pinassertion of the external power-down pin (pdwn/stby) causes the chip to enter full power-down mode. 01 standby pinassertion of the external power-down pin (pdwn/stby) causes the chip to enter standby mode. 10 pin disabledassertion of the external power-down pin (pdwn/stby) is ignored. [5:3] fast detect b/fast detect d (fd_b/fd_d) 0x7 r/w 000 fast detect b/fast detect d output. 001 jesd204b lmfc output. 010 jesd204b internal sync signal in the adc output. 111 disabled (configured as an input with a weak pull down). [2:0] fast detect a/fast detect c (fd_a/fd_c) 0x7 r/w 000 fast detect a/fast detect c output. 001 jesd204b lmfc output. 010 jesd204b internal sync signal in the adc output. 111 disabled (configured as an input with a weak pull down). 0x0108 pair map clock divider control [7:3] reserved reserved. 0x0 r [2:0] clock divider 0x1 r/w 000 divide by 1. 001 divide by 2. 011 divide by 4. 111 divide by 8. 0x0109 channel map clock divider phase [7:4] reserved reserved. 0x0 r [3:0] clock divider phase offset 0x0 r/w 0000 0 input clock cycles delayed. 0001 1/2 input clock cycles delayed (invert clock). 0010 1 input clock cycles delayed. 0011 1 1/2 input clock cycles delayed. 0100 2 input clock cycles delayed. 0101 2 1/2 input clock cycles delayed. 0110 3 input clock cycles delayed. 0111 3 1/2 input clock cycles delayed. 1000 4 input clock cycles delayed. 1001 4 1/2 input clock cycles delayed. 1010 5 input clock cycles delayed. 1011 5 1/2 input clock cycles delayed. 1100 6 input clock cycles delayed. 1101 6 1/2 input clock cycles delayed. 1110 7 input clock cycles delayed. 1111 7 1/2 input clock cycles delayed.
data sheet ad6684 rev. 0 | page 85 of 107 address name bits bit name settings description reset access 0x010a pair map clock divider sysref control 7 clock divider auto phase adjust 0x0 r/w 0 clock divider phase is not changed by sysref (disabled). 1 clock divider phase is automatically adjusted by sysref (enabled). [6:4] reserved reserved. 0x0 r [3:2] clock divider negative skew window 0x0 r/w 00 no negative skew; sysref must be captured accurately. 01 1/2 device clock of negative skew. 10 1 device clocks of negative skew. 11 1 1/2 device clocks of negative skew. [1:0] clock divider positive skew window 0x0 r/w 00 no positive skew; sysref must be captured accurately. 01 1/2 device clock of positive skew. 10 1 device clocks of positive skew. 11 1 1/2 device clocks of positive skew. 0x0110 pair map clock delay control [7:3] reserved reserved. 0x0 r [2:0] clock delay mode select clock delay mode select; used in conjunction with register 0x0111 and register 0x0112. 0x0 r/w 000 no clock delay. 001 reserved. 010 fine delay; only delay step 0 to delay step 16 are valid. 011 fine delay (lowest jitter); only delay step 0 to delay step 16 are valid. 100 fine delay; all 192 delay steps are valid. 101 reserved (same as 001). 110 fine delay enabled; all 192 delay steps are valid. super fine delay enabled (all 128 delay steps are valid). 0x0111 channel map clock super fine delay [7:0] clock super fine delay adjust this is an unsigned control to adjust the super fine sample clock delay in 0.25 ps steps. 0x0 r/w 0x00 0 delay steps. 0x08 8 delay steps. 0x80 128 delay steps. these bits are only used when register 0x0110, bits[2:0] = 0x2 or 0x6. 0x0112 channel map clock fine delay [7:0] clock fine delay adjust clock fine delay adjust. this is an unsigned control to adjust the fine sample clock skew in 1.725 ps steps. 0xc0 r/w 0x00 0 delay steps. 0x08 8 delay steps. 0xc0 192 delay steps. these bits are only used when register 0x0110, bits[2:0] = 0x2, 0x3, 0x4, or 0x6.
ad6684 data sheet rev. 0 | page 86 of 107 address name bits bit name settings description reset access 0x011a clock detection control [7:5] reserved reserved. 0x0 r/w [4:3] clock detection threshold clock detection threshold. 0x1 r/w 01 200 mhz. 11 150 mhz. 2 clock detection enable clock detection enable 0x1 r/w 1 enable. 0 disable. [1:0] reserved. reserved. 0x2 r/w 0x011b pair map clock status [7:1] reserved reserved. 0x0 r 0 input clock detect clock detection status. 0x0 r 0 input clock not detected. 1 input clock detected/locked. 0x011c clock dcs control [7:3] reserved reserved. 0x1 r/w 1 clock dcs enable cl ock dcs enable. 0x0 r/w 0 dcs bypassed. 1 dcs enabled. 0 clock dcs power-up clock dcs power-up. 0x0 r/w 0 dcs powered down. 1 dcs powered up. the dcs must be powered up before being enabled. 0x0120 pair map sysref control 1 7 reserved reserved. 0x0 r 6 sysref flag reset 0 normal flag operation. 0x0 r/w 1 sysref flags held in reset (setup/hold error flags cleared). 5 reserved reserved. 0x0 r 4 sysref transition select 0 sysref is valid on low to high transitions using the selected clk input edge. when changing this setting, the sysref mode select must be set to disabled. 0x0 r/w 1 sysref is valid on high to low transitions using the selected clk input edge. when changing this setting, the sysref mode select must be set to disabled. 3 clk edge select 0 captured on rising edge of clk input. 0x0 r/w 1 captured on falling edge of clk input. [2:1] sysref mode select 00 disabled. 0x0 r/w 01 continuous. 10 n shot. 0 reserved reserved. 0x0 r
data sheet ad6684 rev. 0 | page 87 of 107 address name bits bit name settings description reset access 0x0121 pair map sysref control 2 [7:4] reserved reserved. 0x0 r [3:0] sysref n shot ignore counter select 0000 next sysref only (do not ignore). 0x0 r/w 0001 ignore the first sysref transition. 0010 ignore the first two sysref transitions. 0011 ignore the first three sysref transitions. 0100 ignore the first four sysref transitions. 0101 ignore the first five sysref transitions. 0110 ignore the first six sysref transitions. 0111 ignore the first seven sysref transitions. 1000 ignore the first eight sysref transitions. 1001 ignore the first nine sysref transitions. 1010 ignore the first 10 sysref transitions. 1011 ignore the first 11 sysref transitions. 1100 ignore the first 12 sysref transitions. 1101 ignore the first 13 sysref transitions. 1110 ignore the first 14 sysref transitions. 1111 ignore the first 15 sysref transitions. 0x0123 pair map sysref control 4 7 reserved reserved. 0x0 r [6:0] sysref time stamp delay[6:0] sysref timestamp delay (in converter sample clock cycles) 0x40 r/w 0 0 sample clock cycle delay 1 1 sample clock cycle delay 127 127 sample clock cycle delay 0x0128 pair map sysref status 1 [7:4] sysref hold status[7:4] sysref hold status. see table 37 for more information. 0x0 r [3:0] sysref setup status[3:0] sysref setup status. see table 37 for more information. 0x0 r 0x0129 pair map sysref status 2 [7:4] reserved reserved. 0x0 r [3:0] clock divider phase when sysref is captured sysref divider phase. these bits represent the phase of the divider when sysref is captured. 0x0 r 0000 in phase. 0001 sysref is ? cycle delayed from clock. 0010 sysref is 1 cycle delayed from clock. 0011 1? input clock cycles delayed. 0100 2 input clock cycles delayed. 0101 2? input clock cycles delayed. 1111 7? input clock cycles delayed. 0x012a pair map sysref status 3 [7:0] sysref counter [7:0] (increments when a sysref is captured) sysref count. these bits are a running counter that increments whenever a sysref event is captured. thes bits are reset by register 0x0120, bit 6, and wrap around at 255. read these bits only while register 0x120, bits[2:1] are disabled. 0x0 r
ad6684 data sheet rev. 0 | page 88 of 107 address name bits bit name settings description reset access 0x01ff pair map chip sync [7:1] reserved reserved. 0x0 r 0 synchronization mode 0x0 r/w 0x0 sample synchronization mode. the sysref signal resets all internal sample dividers. use this mode when synchronizing multiple chips as specified in the jesd204b standard. if the phase of any of the dividers must change, the jesd204b link is interrupted. 0x1 partial synchronization/timestamp mode. the sysref signal does not reset sample internal dividers. in this mode, the jesd204b link, the signal monitor, and the parallel interface clocks are not affected by the sysref signal. the sysref signal simply time stamps a sample as it passes through the adc. 0x0200 pair map chip mode [7:6] reserved reserved. 0x0 r/w 5 chip q ignore chip real (i) only selection. 0x0 r/w 0 both real (i) and complex (q) selected. 1 only real (i) selected. complex (q) is ignored. 4 reserved reserved. 0x0 r [3:0] chip application mode 0x7 r/w 0000 full bandwidth mode. 0001 one ddc mode (ddc 0 only). 0010 two ddc mode (ddc 0 and ddc 1 only). 0111 noise shaped requantizer (nsr) mode. 1000 variable dynamic range (vdr) mode. 0x0201 pair map chip dec- imation ratio [7:3] reserved reserved. 0x0 r [2:0] chip decimation ratio select chip decimation ratio. 0x0 r/w 000 decimate by 1 (full sample rate). 001 decimate by 2. 010 decimate by 4. 011 decimate by 8. 100 decimate by 16. 0x0228 channel map custom offset [7:0] offset adjust in lsbs from +127 to ?128 digital datapath offset. twos complement offset adjustment aligned with least significant converter resolution bit. 0x0 r/w 0x0245 channel map fast detect control [7:4] reserved reserved. 0x0 r 3 force fd_a/fd_b/fd_c/ fd_d pins 0x0 r/w 0 normal operation of the fast detect pin. 1 force a value on the fast detect pin (see bit 2 of this register). 2 force value of fd_a/fd_b/ fd_c/fd_d pins; if force pins is true, this value is output on the fast detect pins the fast detect output pin for this channel is set to this valu e when the output is forced. 0x0 r/w 1 reserved reserved. 0x0 r 0 enable fast detect output 0x0 r/w 0 fine fast detect disabled. 1 fine fast detect enabled.
data sheet ad6684 rev. 0 | page 89 of 107 address name bits bit name settings description reset access 0x0247 channel map fast detect upper thres- hold lsb [7:0] fast detect upper threshold [7:0] lsbs of fast detect upper threshold. eight lsbs of the programmable 13-bit upper threshold that is compared to the fine adc magnitude. 0x0 r/w 0x0248 channel map fast detect upper thres- hold msb [7:5] reserved reserved. 0x0 r [4:0] fast detect upper threshold[12:8] lsbs of fast detect upper threshold. eight lsbs of the programmable 13-bit upper threshold that is compared to the fine adc magnitude. 0x0 r/w 0x0249 channel map fast detect lower thres- hold lsb [7:0] fast detect lower threshold[7:0] lsbs of fast detect lower threshold. eight lsbs of the programmable 13-bit lower threshold that is compared to the fine adc magnitude 0x0 r/w 0x024a channel map fast detect lower threshold msb [7:5] reserved reserved. 0x0 r [4:0] fast detect lower threshold[12:8] lsbs of fast detect lower threshold. eight lsbs of the programmable 13-bit lower threshold that is compared to the fine adc magnitude 0x0 r/w 0x024b channel map fast detect dwell time lsb [7:0] fast detect dwell time[7:0] lsbs of fast detect dwell time counter target. this target is a load value for a 16-bit counter that determines how long the adc data must remain below the lower threshold before the fd_x pins are reset to 0 0x0 r/w 0x024c channel map fast detect dwell time msb [7:0] fast detect dwell time[15:8] lsbs of fast detect dwell time counter target. this target is a load value for a 16-bit counter that determines how long the adc data must remain below the lower threshold before the fdd_x pins are reset to 0. 0x0 r/w 0x026f pair map signal monitor sync control [7:2] reserved reserved. 0x0 r 1 reserved reserved. 0x0 r/w 0 signal monitor synchronization mode 0x0 r/w 0 synchronization disabled. 1 only the next valid edge of the sysref pin is used to synchronize the signal monitor block. subsequent edges of the sysref pin are ignored. after the next sysref is received, this bit is cl eared. note that the sysref input pin must be enabled to synchronize the signal monitor blocks. 0x0270 channel map signal monitor control [7:2] reserved reserved. 0x0 r 1 peak detector 0x0 r/w 0 peak detector disabled. 1 peak detector enabled. 0 reserved reserved. 0x0 r 0x0271 channel map signal monitor period 0 [7:0] signal monitor period[7:0] this 24-bit value sets the number of output clock cycles over which the signal monitor performs its operation. bit 0 is ignored. 0x80 r/w 0x0272 channel map signal monitor period 1 [7:0] signal monitor period[15:8] this 24-bit value sets the number of output clock cycles over which the signal monitor performs its operation. bit 0 is ignored. 0x0 r/w 0x0273 channel map signal monitor period 2 [7:0] signal monitor period[23:16] this 24-bit value sets the number of output clock cycles over which the signal monitor performs its operation. bit 0 is ignored. 0x0 r/w
ad6684 data sheet rev. 0 | page 90 of 107 address name bits bit name settings description reset access 0x0274 channel map signal monitor status control [7:5] reserved reserved. 0x0 r 4 result update 0x0 r/w 1 status update based on bits[2:0] (self clearing). 3 reserved reserved. 0x0 r [2:0] result selection 0x1 r/w 001 peak detector placed on status readback signals. 0x0275 channel map signal monitor status 0 [7:0] signal monitor result[7:0] signal monitor status result. this 20-bit value contains the status result calculated by the signal monitor block. the content is dependent on the register 0x0274, bits[2:0] bit settings. 0x0 r 0x0276 channel map signal monitor status 1 [7:0] signal monitor result[15:8] signal monitor status result. this 20-bit value contains the status result calculated by the signal monitor block. the content is dependent on the register 0x0274, bits[2:0] bit settings. 0x0 r 0x0277 channel map signal monitor status 2 [7:4] reserved reserved. 0x0 r [3:0] signal monitor result[19:16] signal monitor status result. this 20-bit value contains the status result calculated by the signal monitor block. the content is dependent on the register 0x0274, bits[2:0] bit settings. 0x0 r 0x0278 channel map signal monitor status frame counter [7:0] period count result[7:0] signal monitor frame counter status bits. the frame counter increments whenever the period counter expires. 0x0 r 0x0279 channel map signal monitor serial framer control [7:2] reserved reserved. 0x0 r 1 reserved reserved. 0x0 r/w 0 signal monitor sport over jesd204b enable 0x0 r/w 0 disabled. 1 enabled. 0x027a channel map signal monitor serial framer input selection [7:6] reserved reserved. 0x0 r [5:0] signal monitor sport over jesd204b peak detector enable 0x2 r/w 1 peak detector enabled.
data sheet ad6684 rev. 0 | page 91 of 107 address name bits bit name settings description reset access 0x0300 pair map ddc sync control [7:6] reserved reserved. 0x0 r/w 5 reserved reserved. 0x0 r 4 ddc nco soft reset this bit can be used to synchronize all the ncos inside the ddc blocks. 0x0 r/w 0 normal operation. 1 ddc held in reset. [3:2] reserved reserved. 0x0 r 1 ddc next sync the sysref pin must be an integer mul- tiple of the nco frequency for this function to operate correctly in continuous mode. 0x0 r/w 0 continuous mode. 1 only the next valid edge of the sysref pin is used to synchronize the nco in the ddc block. subsequent edges of the sysref pin are ignored. aftwr the next sysref is found, the ddc synchronization enable bit is cleared. 0 ddc synchronization mode the sysref input pin must be enabled to synchronize the ddcs. 0x0 r/w 0 synchronization disabled. 1 if the ddc next syncbit = 1, only the next valid edge of the sysref pin is used to synchronize the nco in the ddc block. subsequent edges of the sysref pin are ignored. after the next sysref is received, this bit is cleared. 0x0310 pair map ddc 0 control 7 ddc 0 mixer select 0x0 r/w 0 real mixer (i and q inputs must be from the same real channel). 1 complex mixer (i and q must be from separate real and imaginary quadrature adc receive channelsanalog demodulator). 6 ddc 0 gain select gain can be used to compensate for the 6 db loss associated with mixing an input signal down to baseband and filtering out its negative component. 0x0 r/w 0 0 db gain. 1 6 db gain (multiply by 2). [5:4] ddc 0 if mode 0x0 r/w 00 variable if mode. 01 0 hz if mode. 10 f s /4 hz if mode. 11 test mode. 3 ddc 0 complex to real enable 0x0 r/w 0 complex (i and q) outputs contain valid data. 1 real (i) output only. complex to real enabled. uses extra f s /4 mixing to convert to real. 2 reserved reserved. 0x0 r
ad6684 data sheet rev. 0 | page 92 of 107 address name bits bit name settings description reset access [1:0] ddc 0 decimation rate select decimation filter selection. complex outputs (complex to real disabled): 0x0 r/w 11 hb1 filter selection (decimate by 2). 00 hb2 + hb1 filter selection (decimate by 4). 01 hb3 + hb2 + hb1 filter selection (decimate by 8). 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 16). real outputs (compl ex to real enabled): 11 hb1 filter selection (decimate by 1). 00 hb2 + hb1 filter selection (decimate by 2). 01 hb3 + hb2 + hb1 filter selection (decimate by 4). 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 8). 11 hb1 filter selection: decimate by 1 or 2. 00 hb2 + hb1 filter selection (decimate by 2 or 4). 01 hb3 + hb2 + hb1 filter selection (decimate by 4 or 8) 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 8 or 16) 0x0311 pair map ddc 0 input select [7:3] reserved reserved. 0x0 r 2 ddc 0 q input select 0x0 r/w 0 channel a. 1 channel b. 1 reserved reserved. 0x0 r 0 ddc 0 i input select 0x0 r/w 0 channel a. 1 channel b. 0x0314 pair map ddc 0 phase increment 0 [7:0] ddc 0 nco frequency value, twos complement[7:0] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x0315 pair map ddc 0 phase increment 1 [7:0] ddc 0 nco frequency value, twos complement[15:8] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc_phase_inc f s )/2 48 . 0x0 r/w 0x0316 pair map ddc 0 phase increment 2 [7:0] ddc 0 nco frequency value, twos complement[23:16] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc_phase_inc f s )/2 48 . 0x0 r/w 0x0317 pair map ddc 0 phase increment 3 [7:0] ddc 0 nco frequency value, twos complement[31:24] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc_phase_inc f s )/2 48 . 0x0 r/w 0x0318 pair map ddc 0 phase increment 4 [7:0] ddc 0 nco frequency value, twos complement[39:32] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc_phase_inc f s )/2 48 . 0x0 r/w 0x031a pair map ddc 0 phase increment 5 [7:0] ddc 0 nco frequency value, twos complement[47:40] nco phase increment value; twos complement phase increment value for the nco. complex mixing frequency = (ddc_phase_inc f s )/2 48 . 0x0 r/w 0x031d pair map ddc 0 phase offset 0 [7:0] ddc 0 nco phase value, twos complement[7:0] twos complement phase offset value for the nco. 0x0 r/w
data sheet ad6684 rev. 0 | page 93 of 107 address name bits bit name settings description reset access 0x031e pair map ddc 0 phase offset 1 [7:0] ddc 0 nco phase value, twos complement[15:8] twos complement phase offset value for the nco. 0x0 r/w 0x031f pair map ddc 0 phase offset 2 [7:0] ddc 0 nco phase value, twos complement[23:16] twos complement phase offset value for the nco. 0x0 r/w 0x0320 pair map ddc 0 phase offset 3 [7:0] ddc 0 nco phase value, twos complement[31:24] twos complement phase offset value for the nco. 0x0 r/w 0x0321 pair map ddc 0 phase offset 4 [7:0] ddc 0 nco phase value, twos complement[39:32] twos complement phase offset value for the nco. 0x0 r/w 0x0322 pair map ddc 0 phase offset 5 [7:0] ddc 0 nco phase value, twos complement[47:40] twos complement phase offset value for the nco. 0x0 r/w 0x0327 pair map ddc 0 test enable [7:3] reserved reserved. 0x0 r 2 ddc 0 q output test mode enable q samples always use the test mode b/ test mode d block. 0x0 r/w 0 test mode disabled. 1 test mode enabled. 1 reserved reserved. 0x0 r 0 ddc 0 i output test mode enable i samples always use test mode a/ test mode c block. 0x0 r/w 0 test mode disabled. 1 test mode enabled. 0x0330 pair map ddc 1 control 7 ddc 1 mixer select 0x0 r/w 0 real mixer (i and q inputs must be from the same real channel). 1 complex mixer (i and q must be from separate, real and imaginary quadrature adc receive channelsanalog demodulator). 6 ddc 1 gain select gain can be used to compensate for the 6 db loss associated with mixing an input signal down to baseband and filtering out its negative component. 0x0 r/w 0 0 db gain. 1 6 db gain (multiply by 2). [5:4] ddc 1 if mode 0x0 r/w 00 variable if mode. 01 0 hz if mode. 10 f s /4 hz if mode. 11 test mode. 3 ddc 1 complex to real enable 0x0 r/w 0 complex (i and q) outputs contain valid data. 1 real (i) output only. complex to real enabled. uses extra f s /4 mixing to convert to real. 2 reserved reserved. 0x0 r
ad6684 data sheet rev. 0 | page 94 of 107 address name bits bit name settings description reset access [1:0] ddc 1 decimation rate select decimation filter selection. complex outputs (complex to real disabled): 0x0 r/w 11 hb1 filter selection (decimate by 2). 00 hb2 + hb1 filter selection (decimate by 4). 01 hb3 + hb2 + hb1 filter selection (decimate by 8). 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 16). real outputs (compl ex to real enabled): 11 hb1 filter selection (decimate by 1). 00 hb2 + hb1 filter selection (decimate by 2). 01 hb3 + hb2 + hb1 filter selection (decimate by 4). 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 8). 11 hb1 filter selection: decimate by 1 or 2. 00 hb2 + hb1 filter selection (decimate by 2 or 4). 01 hb3 + hb2 + hb1 filter selection (decimate by 4 or 8) 10 hb4 + hb3 + hb2 + hb1 filter selection (decimate by 8 or 16) 0x0331 pair map ddc 1 input select [7:3] reserved reserved. 0x0 r 2 ddc 1 q input select 0x1 r/w 0 channel a. 1 channel b. 1 reserved reserved. 0x0 r 0 ddc 1 i input select 0x1 r/w 0 channel a. 1 channel b. 0x0334 pair map ddc 1 phase increment 0 [7:0] ddc 1 nco frequency value, twos complement[7:0] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x0335 pair map ddc 1 phase increment 1 [7:0] ddc 1 nco frequency value, twos complement[15:8] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x0336 pair map ddc 1 phase increment 2 [7:0] ddc 1 nco frequency value, twos complement[23:16] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x0337 pair map ddc 1 phase increment 3 [7:0] ddc 1 nco frequency value, twos complement[31:24] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x0338 pair map ddc 1 phase increment 4 [7:0] ddc 1 nco frequency value, twos complement[39:32] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x033a pair map ddc 1 phase increment 5 [7:0] ddc 1 nco frequency value, twos complement[47:40] nco phase increment value. twos complement phase increment value for the nco. complex mixing frequency = (ddc phase increment f s )/2 48 . 0x0 r/w 0x033d pair map ddc 1 phase offset 0 [7:0] ddc 1 nco phase value, twos complement[7:0] twos complement phase offset value for the nco. 0x0 r/w
data sheet ad6684 rev. 0 | page 95 of 107 address name bits bit name settings description reset access 0x033e pair map ddc 1 phase offset 1 [7:0] ddc 1 nco phase value, twos complement[15:8] twos complement phase offset value for the nco. 0x0 r/w 0x033f pair map ddc 1 phase offset 2 [7:0] ddc 1 nco phase value, twos complement[23:16] twos complement phase offset value for the nco. 0x0 r/w 0x0340 pair map ddc 1 phase offset 3 [7:0] ddc 1 nco phase value, twos complement[31:24] twos complement phase offset value for the nco. 0x0 r/w 0x0341 pair map ddc 1 phase offset 4 [7:0] ddc 1 nco phase value, twos complement[39:32] twos complement phase offset value for the nco. 0x0 r/w 0x0342 pair map ddc 1 phase offset 5 [7:0] ddc 1 nco phase value, twos complement[47:40] twos complement phase offset value for the nco. 0x0 r/w 0x0347 pair map ddc 1 test enable [7:3] reserved reserved. 0x0 r 2 ddc 1 q output test mode enable q samples always use the test mode b/ test mode d block. 0x0 r/w 0 test mode disabled. 1 test mode enabled. 1 reserved reserved. 0x0 r 0 ddc 1 i output test mode enable i samples always use the test mode a/ test mode c block. 0x0 r/w 0 test mode disabled. 1 test mode enabled. 0x041e channel map nsr decimate by 2 control 7 high-pass/low-pass mode decimate by 2 high-pass/low-pass mode. 0x0 r/w 0 enable lpf. 1 enable hpf. 6 reserved reserved. 0x0 r [5:4] reserved reserved. 0x0 r/w [3:1] reserved reserved. 0x0 r 0 nsr decimate by 2 enable 0x0 r/w 0 decimate by 2 disabled. 1 decimate by 2 enabled. 0x0420 nsr mode 7 reserved reserved. 0x0 r/w [6:4] reserved reserved. 0x0 r [3:1] nsr mode 0x0 r/w 000 21% bw mode. 001 28% bw mode. 0 reserved reserved. 0x0 r 0x0422 channel map nsr tuning [7:6] reserved reserved. 0x0 r [5:0] nsr tuning word noise shaped requantizer tuning frequency (see the noise shaping requantizer (nsr) section for details). 0x0 r/w
ad6684 data sheet rev. 0 | page 96 of 107 address name bits bit name settings description reset access 0x0430 pair map vdr control 7 reserved reserved. 0x0 r/w [6:5] reserved reserved. 0x0 r 4 reserved reserved. 0x0 r/w [3:2] reserved reserved. 0x0 r 1 vdr bandwidth 0x0 r/w 0 25% bw mode. 1 43% bw mode. only available in complex mode. 0 vdr complex mode enable 0x1 r/w 0 dual real mode. ignore bit 1. 1 dual complex mode. complex input, channel a/channel c are i and channel b/channel d are q. 0x0434 channel map vdr tuning frequency [7:4] reserved reserved. 0x0 r [3:0] vdr center frequency see the variable dynamic range (vdr) section for details. 0x0 r/w 0x0550 channel map test mode control 7 user pattern selection 0x0 r/w 0 continuous repeat. 1 single pattern. 6 reserved reserved. 0x0 r 5 reset pn long generation 0x0 r/w 0 long pn enabled. 1 long pn held in reset. 4 reset pn short generation 0x0 r/w 0 short pn enabled. 1 short pn held in reset. [3:0] test mode selection 0x0 r/w 0000 offnormal operation. 0001 midscale short. 0010 positive full scale. 0011 negative full scale. 0100 alternating checker board. 0101 pn sequencelong. 0110 pn sequenceshort. 0111 1/0 word toggle. 1000 user pattern test mode (used with the test mode patern selection and the user pattern 1 through user pattern 4 registers) 1111 ramp output. 0x0551 pair map user pattern 1 lsb [7:0] user pattern 1[7:0] user test pattern 1 least significant byte 0x0 r/w 0x0552 pair map user pattern 1 msb [7:0] user pattern 1[15:8] user test pattern 1 most significant byte 0x0 r/w 0x0553 pair map user pattern 2 lsb [7:0] user pattern 2[7:0] user test pattern 2 least significant byte 0x0 r/w 0x0554 pair map user pattern 2 msb [7:0] user pattern 2[15:8] user test pattern 2 most significant byte 0x0 r/w 0x0555 pair map user pattern 3 lsb [7:0] user pattern 3[7:0] user test pattern 3 least significant byte 0x0 r/w
data sheet ad6684 rev. 0 | page 97 of 107 address name bits bit name settings description reset access 0x0556 pair map user pattern 3 msb [7:0] user pattern 3[15:8] user test pattern 3 most significant byte 0x0 r/w 0x0557 pair map user pattern 4 lsb [7:0] user pattern 4[7:0] user test pattern 4 least significant byte 0x0 r/w 0x0558 pair map user pattern 4 msb [7:0] user pattern 4[15:8] user test pattern 4 most significant byte 0x0 r/w 0x0559 pair map output control mode 0 7 reserved reserved. 0x0 r [6:4] converter control bit 1 selection 0x0 r/w 000 tie low (1'b0). 001 overrange bit. 010 signal monitor bit or vdr punish bit 0. 011 fast detect (fd) bit or vdr punish bit 1. 100 vdr high/low resolution bit. 101 sysref. 110 reserved. 111 reserved. 3 reserved reserved. 0x0 r [2:0] converter control bit 0 selection 0x0 r/w 000 tie low (1'b0) 001 overrange bit. 010 signal monitor or vdr punish bit 0. 011 fast detect (fd) bit or vdr punish bit 1. 100 vdr high/low resolution bit. 101 sysref. 0x055a pair map output control mode 1 [7:3] reserved reserved. 0x0 r [2:0] converter control bit 2 selection 0x1 r/w 000 tie low (1'b0). 001 overrange bit. 010 signal monitor bit or vdr punish bit 0. 011 fast detect (fd) bit or vdr punish bit 1. 100 vdr high/low resolution bit. 101 sysref. 110 reserved. 111 reserved. 0x0561 pair map output sample mode [7:3] reserved reserved. 0x0 r 2 sample invert 0x0 r/w 0 adc sample data is not inverted. 1 adc sample data is inverted. [1:0] data format select 0x1 r/w 00 offset binary. 01 twos complement (default). 0x0564 pair map output channel select [7:2] reserved reserved. 0x0 r 1 reserved reserved. 0x0 r/w 0 converter channel swap control 0x0 r/w 0 normal channel ordering. 1 channel swap enabled.
ad6684 data sheet rev. 0 | page 98 of 107 address name bits bit name settings description reset access 0x056e jesd204b map pll control [7:4] jesd204b lane rate control 0x0 r/w 0000 lane rate = 6.75 to 13.5 gbps. 0001 lane rate = 3.375 gbps to 6.75 gbps. 0011 lane rate = 13.5 to 15 gbps. 0101 lane rate = 1.6875 gbps to 3.375 gbps. [3:0] reserved reserved. 0x0 r 0x056f jesd204b map pll status 7 pll lock status 0x0 r 0 not locked. 1 locked. [6:4] reserved reserved. 0x0 r 3 reserved reserved. 0x0 r [2:0] reserved reserved. 0x0 r 0x0570 jesd204b map jtx quick config- uration [7:6] quick configuration l number of lanes (l) = 2 register0x0570, bits[7:6] 0x1 r/w 0 l = 1. 1 l = 2. [5:3] quick configuration m number of converters (m) = 2 register 0x0570, bits[5:3] 0x1 r/w 0 m = 1. 1 m = 2. 10 m = 4. [2:0] quick configuration f number of octets/frame (f) = 2 register 0x0570, bits[2:0] 0x1 r/w 0 f = 1. 1 f = 2. 10 f = 4. 11 f = 8. 0x0571 jesd204b map jtx link control 1 7 standby mode 0x0 r/w 0 standby mode forces zeros for all converter samples. 1 standby mode forces code group synchronization (k28.5 characters). 6 tail bit (t) pn 0x0 r/w 0 disable. 1 enable. 5 long transport layer test 0x0 r/w 0 jesd204b test samples disabled. 1 jesd204b test samples enabled. the long transport layer test sample sequence (as specified in jesd204b section 5.1.6.3) sent on all link lanes. 4 lane synchronization 0x1 r/w 0 disable faci uses /k28.7/. 1 enable faci uses /k28.3/ and /k28.7/. [3:2] ilas sequence mode 0x1 r/w 00 initial lane alignment sequence disabled (see jesd204b section 5.3.3.5). 01 initial lane alignment sequence enabled (see jesd204b section 5.3.3.5). 11 initial lane alignment sequence always on test mode. jesd204b data link layer test mode where repeated lane alignment sequence (as specified in jesd204b, section 5.3.3.8.2) sent on all lanes.
data sheet ad6684 rev. 0 | page 99 of 107 address name bits bit name settings description reset access 1 faci 0x0 r/w 0 frame alignment character insertion enabled (jesd204b, section 5.3.3.4). 1 frame alignment character insertion disabled; for debug only (jesd204b, section 5.3.3.4) 0 link control 0x0 r/w 0 jesd204b serial transmit link enabled. transmission of the /k28.5/ characters for code group synchronization is controlled by the syncinbx signal pin. 1 jesd204b serial transmit link powered down (held in reset and clock gated). 0x0572 jesd204b map jtx link control 2 [7:6] syncinbab/ syncinbcd pin control 0x0 r/w 00 normal mode. 10 ignore syncinbab/syncinbcd (force cgs). 11 ignore syncinbab/syncinbcd (force ilas/user data). 5 syncinbab/ syncinbcd pin invert 0x0 r/w 0 syncinbab/syncinbcd pin not inverted. 1 syncinbab/syncinbcd pin inverted. 4 syncinbab/ syncinbcd pin type 0x0 r/w 0 lvds differential pair sync signal input. 1 cmos single-ended sync signal input. 3 reserved reserved. 0x0 r 2 8-bit/10-bit bypass 0x0 r/w 0 8-bit/10-bit enabled. 1 8-bit/10-bit bypassed (the most significant two bits are 0). 1 8-bit/10-bit bit invert 0x0 r/w 0 normal. 1 invert a b c d e f g h i j symbols. 0 reserved reserved. 0x0 r/w 0x0573 jesd204b map jtx link control 3 [7:6] checksum mode 0x0 r/w 00 checksum is the sum of all the 8-bit registers in the link configuration table. 01 checksum is the sum of all individual link configuration fields (lsb aligned). 10 checksum is disabled (set to 0). for test purposes only. 11 unused. [5:4] test injection point 0x0 r/w 0 n' sample input. 1 10-bit data at 8-bit/10-bit output (for phy testing). 10 8-bit data at scrambler input.
ad6684 data sheet rev. 0 | page 100 of 107 address name bits bit name settings description reset access [3:0] jesd204b test mode patterns 0x0 r/w 0 normal operation(test mode disabled). 1 alternating checkerboard. 10 1/0 word toggle. 11 31-bit pn sequence: x 31 + x 28 + 1. 100 23-bit pn sequence: x 23 + x 18 + 1. 101 15-bit pn sequence: x 15 + x 14 + 1. 110 9-bit pn sequence: x 9 + x 5 + 1. 111 7-bit pn sequence: x 7 + x 6 + 1. 1000 ramp output. 1110 continuous/repeat user test. 1111 single user test. 0x0574 jesd204b map jtx link control 4 [7:4] ilas delay 0x0 r/w 0 transmit ilas on first lmfc after syncinbx is deasserted. 1 transmit ilas on second lmfc after syncinb is deasserted. 10 transmit ilas on third lmfc after syncinbx is deasserted. 11 transmit ilas on fourth lmfc after syncinb is deasserted. 100 transmit ilas on fifth lmfc after syncinbx is deasserted. 101 transmit ilas on sixth lmfc after syncinbx is deasserted. 110 transmit ilas on seventh lmfc after syncinbx is deasserted. 111 transmit ilas on eightth lmfc after syncinbx is deasserted. 1000 transmit ilas on nineth lmfc after syncinbx is deasserted. 1001 transmit ilas on 10th lmfc after syncinbx is deasserted. 1010 transmit ilas on 11th lmfc after syncinbx is deasserted. 1011 transmit ilas on 12th lmfc after syncinbx is deasserted. 1100 transmit ilas on 13th lmfc after syncinbx is deasserted. 1101 transmit ilas on 14th lmfc after syncinbx is deasserted. 1110 transmit ilas on 15th lmfc after syncinbx is deasserted. 1111 transmit ilas on 16th lmfc after syncinbx is deasserted. 3 reserved reserved. 0x0 r [2:0] link layer test mode 0x0 r/w 000 normal operation (link layer test mode disabled). 001 continuous sequence of /d21.5/ characters. 010 reserved. 011 reserved. 100 modified rpat test sequence. 101 jspat test sequence. 110 jtspat test sequence. 111 reserved.
data sheet ad6684 rev. 0 | page 101 of 107 address name bits bit name settings description reset access 0x0578 jesd204b map jtx lmfc offset [7:5] reserved reserved. 0x0 r [4:0] lmfc phase offset value lmfc phase offset value; reset value for lmfc phase counter when sysref is asserted. used for deterministic delay applications. 0x0 r/w 0x0580 jesd204b map jtx did config- uration [7:0] jesd204b tx did value jesd204b serial device identification (did) number. 0x0 r/w 0x0581 jesd204b map jtx bid config- uration [7:4] reserved reserved. 0x0 r [3:0] jesd204b tx bid value jesd204b serial bank identification (bid) number (extension to did). 0x0 r/w 0x0583 jesd204b map jtx lid0 config- uration [7:5] reserved reserved. 0x0 r [4:0] lane 0 lid value jesd204b serial lane identification (lid) number for lane 0. 0x0 r/w 0x0585 jesd204b map jtx lid1 config- uration [7:5] reserved reserved. 0x0 r [4:0] lane 1 lid value jesd204b serial lane identification (lid) number for lane 1. 0x2 r/w 0x058b jesd204b map jtx scr l config- uration 7 jesd204b scrambling (scr) 0x1 r/w 0 jesd204b scrambler disabled. scr = 0. 1 jesd204b scrambler enabled. scr = 1. [6:5] reserved reserved. 0x0 r [4:0] jesd204b lanes (l) 0x1 r 0x0 one lane per link (l = 1). 0x1 two lanes per link (l = 2). 0x058c jesd204b map jtx f config- uration [7:0] number of octets per frame (f) number of octets per frame. f = register 0x058c, bits[7:0] + 1. 0x1 r 0x058d jesd204b map jtx k config- uration [7:5] reserved reserved. 0x0 r [4:0] number of frames per multiframe (k) jesd204b number of frames per multi- frame (k = register 0x058d, bits[4:0] + 1). only values where f k are divisible by 4 can be used. 0x1f r/w 00011 k = 4. 00111 k = 8. 01100 k = 12. 01111 k = 16. 10011 k = 20. 10111 k = 24. 11011 k = 28. 11111 k = 32. 0x058e jesd204b map jtx m config- uration [7:0] number of converters per link 0x1 r 00000000 link connected to one virtual converter (m = 1). 00000001 link connected to two virtual converters (m = 2). 00000011 link connected to four virtual converters (m = 4).
ad6684 data sheet rev. 0 | page 102 of 107 address name bits bit name settings description reset access 0x058f jesd204b map jtx cs n config- uration [7:6] number of control bits (cs) per sample 0x0 r/w 0 no control bits (cs = 0). 1 one control bit (cs = 1), control bit 2 only. 10 two control bits (cs = 2), control bit 2 and control bit 1 only. 11 three control bits (cs = 3), all control bits (bits[2:0]). 5 reserved reserved. 0x0 r [4:0] adc converter resolution (n) 0xf r/w 00110 n = 7-bit resolution. 00111 n = 8-bit resolution. 01000 n = 9-bit resolution. 01001 n = 10-bit resolution. 01010 n = 11-bit resolution. 01011 n = 12-bit resolution. 01100 n = 13-bit resolution. 01101 n = 14-bit resolution. 01110 n = 15-bit resolution. 01111 n = 16-bit resolution. 0x0590 jesd204b map jtx scv np config- uration [7:5] subclass support 0x1 r/w 000 subclass 0. 001 subclass 1. [4:0] adc number of bits per sample (n') 0xf r/w 00111 n' = 8. 01111 n' = 16. 0x0591 jesd204b map jtx jv s config- uration [7:5] reserved reserved. 0x1 r [4:0] samples per converter frame cycle (s) samples per converter frame cycle (s = register 0x0591, bits[4:0] + 1). 0x0 r 0x0592 jesd204b map jtx hd cf config- uration 7 hd value 0x0 r 0 high density format disabled. 1 high density format enabled. [6:5] reserved reserved. 0x0 r [4:0] control words per frame clock cycle per link (cf) number of control words per frame clock cycle per link (cf = register 0x0592, bits[4:0]). 0x0 r 0x05a0 jesd204b map jtx checksum 0 config- uration [7:0] checksum 0 checksum value for serdoutab0/ serdoutcd0 serial checksum value for lane 0, auto- matically calculated for each lane. sum (all link configuration parameters for lane 0) mod 256. 0xc3 r 0x05a1 jesd204b map jtx checksum 1 config- uration [7:0] checksum 1 checksum value for serdoutab1/ serdoutcd1 serial checksum value for lane 1, auto- matically calculated for each lane. sum (all link configuration parameters for lane 1) mod 256. 0xc4 r 0x05b0 jesd204b map jtx lane power- down [7:3] reserved reserved. 0x1f r/w 2 jesd204b lane 1 power- down physical lane 1 force power-down. 0x0 r/w 1 reserved reserved. 0x1 r/w 0 jesd204b lane 0 power- down physical lane 0 force power-down. 0x0 r/w
data sheet ad6684 rev. 0 | page 103 of 107 address name bits bit name settings description reset access 0x05b2 jesd204b map jtx lane assign- ment 1 7 reserved reserved. 0x0 r [6:4] reserved reserved. 0x0 r/w 3 reserved reserved. 0x0 r [2:0] serdoutab0/ serdoutcd0 lane assignment 0x0 r/w 0 logical lane 0 (default). 1 logical lane 1. 0x05b3 jesd204b map jtx lane assign- ment 2 7 reserved reserved. 0x0 r [6:4] reserved reserved. 0x1 r/w 3 reserved reserved. 0x0 r [2:0] serdoutab1/ serdoutcd1 lane assignment 0x1 r/w 0 logical lane 0. 1 logical lane 1 (default). 0x05c0 jesd204b map jesd204b serializer drive adjust 7 reserved reserved. 0x0 r [6:4] swing voltage for serdoutab1/ serdoutcd1 0x1 r/w 0 1.0 drvdd1 (differential). 1 0.850 drvdd1 (differential). 3 reserved reserved. 0x0 r [2:0] swing voltage for serdoutab0/ serdoutcd0 0x1 r/w 0 1.0 drvdd1 (differential). 0x05c4 jesd204b serializer preemphasis selection register for logical lane 0 7 post tab polarity post tab polarity. 0x0 r/w 0 normal. 1 inverted. [6:4] sets post tab level these bi ts set the post tab level. 0x0 r/w 0 0 db. 1 3 db. 10 6 db. 11 9 db. 100 12 db. 101 not valid. 110 not valid. 111 not valid. 3 pretab polarity pretab polarity. 0x0 r/w 0 normal. 1 inverted. [2:0] sets pretab level these bits set the pretab level. 0x0 r/w 0 0 db. 1 3 db. 10 6 db. 11 9 db. 100 12 db. 101 not valid. 110 not valid. 111 not valid.
ad6684 data sheet rev. 0 | page 104 of 107 address name bits bit name settings description reset access 0x05c6 jesd204b serializer preemphasis selection register for logical lane 1 7 post tab polarity post tab polarity. 0x0 r/w 0 normal. 1 inverted. [6:4] sets post tab level these bi ts set the post tab level. 0x0 r/w 0 0 db. 1 3 db. 10 6 db. 11 9 db. 100 12 db. 101 not valid. 110 not valid. 111 not valid. 3 pretab polarity this bit se ts the pretab polarity. 0x0 r/w 0 normal. 1 inverted. [2:0] sets pretab level these bits set the pretab level. 0x0 r/w 0 0 db. 1 3 db. 10 6 db. 11 9 db. 100 12 db. 101 not valid. 110 not valid. 111 not valid. 0x0922 large dither control [7:0] large dither control enables/disa bles the large dither control. 0x70 r/w 1110000 enable. 1110001 disable. 0x1222 pll calibration [7:0] pll calibration pll calibration. 0x0 r/w 0x00 normal operation. 0x04 pll calibration 0x1228 jesd204b start-up circuit reset [7:0] jesd204b start-up circuit reset jesd204b start-up circuit reset. 0xf r/w 0x0f normal operation. 0x4f start-up circuit reset. 0x1262 pll loss of lock control pll loss of lock control pll loss of lock control. 0x0 r/w 0x00 normal operation. 0x08 clear loss of lock. 0x18a6 pair map vref control [7:5] reserved reserved. 0x0 r 4 reserved reserved. 0x0 r/w [3:1] reserved reserved. 0x0 r 0 vref control 0x0 r/w 0 internal reference. 1 external reference. 0x1908 channel map analog input control [7:6] reserved reserved. 0x0 r [5:4] reserved reserved. 0x0 r/w 3 reserved reserved. 0x0 r 2 analog input dc coupling control analog input dc coupling control. 0x0 r/w 0 ac coupling. 1 dc coupling. 1 reserved reserved. 0x0 r 0 reserved reserved. 0x0 r/w
data sheet ad6684 rev. 0 | page 105 of 107 address name bits bit name settings description reset access 0x1910 channel map input full-scale range [7:4] reserved reserved. 0x0 r [3:0] input full-scale control input full-scale control 0xd r/w 0000 2.16 v p-p. 1010 1.44 v p-p. 1011 1.56 v p-p. 1100 1.68 v p-p. 1101 1.80 v p-p. 1110 1.92 v p-p. 1111 2.04 v p-p. 0x1a4c channel map buffer control 1 [7:6] reserved reserved. 0x0 r [5:0] buffer control 1 buffer control 1. 0xc r/w 00110 120 a. 01000 160 a. 01010 200 a. 01100 240 a. 01110 280 a. 10000 320 a. 10010 360 a. 10100 400 a. 10110 440 a. 0x1a4d channel map buffer control 2 [7:6] reserved reserved. 0x0 r [5:0] buffer control 2 buffer control 2. 0xc r/w 00110 120 a. 01000 160 a. 01010 200 a. 01100 240 a. 01110 280 a. 10000 320 a. 10010 360 a. 10100 400 a. 10110 440 a. 0x18e0 external vcm buffer control 1 [7:0] external vcm buffer control 1 see the input common mode section for details. 0x0 r/w 0x18e1 external vcm buffer control 2 [7:0] external vcm buffer control 2 see the input common mode section for details. 0x0 r/w 0x18e2 external vcm buffer control 3 [7:0] external vcm buffer control 3 see the input common mode section for details. 0x0 r/w 0x18e3 external vcm buffer control 7 reserved reserved. 0x0 r/w 6 external vcm buffer external vcm buffer. 0x0 r/w 1 enable. 0 disable. [5:0] external vcm buffer current setting see the input common mode section for details. 0x0 r/w 0x18e6 temperature diode export [7:1] reserved reserved. 0x0 r/w 0 temperature diode export temperature diode export. 0x0 r/w 1 enable. 0 disable.
ad6684 data sheet rev. 0 | page 106 of 107 applications information power supply recommendations the ad6684 must be powered by the following seven supplies: avdd1 = avdd1_sr = 0.975 v, avdd2 = 1.8 v, avdd3 = 2.5 v, dvdd = 0.975 v, drvdd1 = 0.975 v, and spivdd = 1.8 v. for applications requiring an optimal high power efficiency and low noise performance, it is recommended that the adp5054 quad switching regulator be used to convert the 6.0 v or 12 v input rails to intermediate rails (1.3 v, 2.4 v, and 3.0 v). these intermediate rails are then postregulated by very low noise, low dropout (ldo) regulators ( adp1762 , adp7159 , adp151 , and adp7118 ). figure 104 shows the recommended power supply scheme for the ad6684. avdd1: 0.95v 1.3v avdd1_sr: 0.95v adp1762 (ldo) adp1762 (ldo) adp7159 (ldo) adp7159 (ldo) dvdd: 0.95v drvdd1: 0.95v avdd2: 1.8v avdd3: 2.5v drvdd2: 1.8v 6v/12 v input spivdd: 1.8v 2.4v adp151 (ldo) 1.3v filter filter filter filter filter filter adp7118 (ldo) filter 3.0v 14994-091 adp5054 (switching regulator) figure 104. high efficiency, low noise power solution for the ad6684 it is not necessary to split all of these power domains in all cases. the recommended solution shown in figure 104 provides the lowest noise, highest efficiency power delivery system for the ad6684 . if only one 0.975 v supply is available, route to avdd1 first and then tap it off and isolate it with a ferrite bead or a filter choke, preceded by decoupling capacitors for avdd1_sr, dvdd, and drvdd, in that order. the user can employ several different decoupling capacitors to cover both high and low frequencies. these capacitors must be located close to the point of entry at the pcb level and close to the devices, with minimal trace lengths. exposed pad thermal heat slug recommendations it is required that the exposed pad on the underside of the adc be connected to agnd to achieve the best electrical and thermal performance of the ad6684 . connect an exposed continuous copper plane on the pcb to the ad6684 exposed pad, pin 0. the copper plane must have several vias to achieve the lowest possible resistive thermal path for heat dissipation to flow through the bottom of the pcb. these vias must be solder filled or plugged. the number of vias and the fill determine the resultant ja measured on the board (see table 7). see figure 105 for a pcb layout example. for detailed information on packaging and the pcb layout of chip scale packages, see the an-772 application note , a design and manufacturing guide for the lead frame chip scale package (lfcsp) . 14994-092 figure 105. recommended pcb layout of exposed pad for the ad6684 avdd1_sr (pin 64) an d agnd_sr (pin 63 and pin 67) avdd1_sr (pin 64) and agnd_sr (pin 63 and pin 67) can be used to provide a separate power supply node to the sysref circuits of the ad6684 . if running in subclass 1, the ad6684 can support periodic one-shot or gapped signals. to minimize the coupling of this supply into the avdd1 supply node, adequate supply bypassing is needed.
data sheet ad6684 rev. 0 | page 107 of 107 outline dimensions compliant to jedec standards mo-220-vnnd-4 1.00 0.85 0.80 1 18 54 37 19 36 72 55 0.50 0.40 0.30 8.50 ref pin 1 indicator seating plane 12 max 0.60 0.42 0.24 0.60 0.42 0.24 0.30 0.23 0.18 0.50 bsc pin 1 indicator coplanarity 0.08 06-30-2015-a for proper connection of the exposed pad, refer to the pin configuration and function descriptions section of this data sheet. 10.10 10.00 sq 9.90 9.85 9.75 sq 9.65 0.20 min 7.45 7.30 sq 7.15 top view bottom view exposed pad pkg-004890 0.05 max 0.02 nom 0.80 max 0.65 nom 0.20 nom figure 106. 72-lead lead frame chip scale package [lfcsp] 10 mm 10 mm body and 0.85 mm package height (cp-72-10) dimensions shown in millimeters ordering guide model 1 junction temperature range package description package option ad6684bcpz-500 ?40c to +105c 72-lead lead frame chip scale package [lfcsp] cp-72-10 AD6684BCPZRL7-500 ?40c to +105c 72-lead lead frame chip scale package [lfcsp] cp-72-10 ad6684-500ebz evaluation board for ad6684 1 z = rohs compliant part. ?2016 analog devices, inc. all rights reserved. trademarks and registered trademarks are the property of their respective owners. d14994-0-10/16(0)

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